* perf(search_text): precompute line offsets for O(log n) line lookup

search_for_pattern resolved each match's line number by rescanning the
file from the beginning (TextUtils.get_line_from_index walks a
TextStepper from index 0), making coordinate resolution O(n) per match
and O(n*m) for m matches. search_text now precomputes line start
offsets once per file (O(n)) and resolves each match via binary search
(O(log n) per match).

The precomputed table mirrors TextStepper line semantics exactly:
\n, \r\n and bare \r are line separators, and an index pointing at the
\n of a \r\n pair resolves to (next line, 0) — the same rule
TextUtils.get_line_col_from_index implements, now pinned by regression
tests (including the mixed line-ending edge cases from the
insert_text_at_position fix).

On a synthetic 12k-line file (494 KB) with 723 matches, match-coordinate
resolution drops from ~1764 ms to ~2 ms (~1000x); the one-off
precompute costs ~1.1 ms. Small files regress nothing (100 lines, 5
matches: 70 µs -> 11 µs). Results are byte-for-byte identical to the
previous implementation.

Note: compatible with PR #1899 (interruptible agent regexes): that PR
touches the re.compile call site in search_text and the ContentReplacer
helpers, this PR touches the post-match line-coordinate resolution; the
two changes are complementary and rebase cleanly onto each other.

* perf(search_text): add reproducible benchmark script

scripts/profile_search_text.py regenerates the synthetic benchmark
content with a fixed seed (no real-world code), asserts both resolution
paths produce identical results, and prints the before/after timings
quoted in the PR description. Default: 12k lines / ~1830 matches;
optional CLI args scale the file down for quick runs.

* refactor(ls): encapsulate cached text coordinates in TextCoordinates abstraction

Address review feedback on the search_text line-lookup PR: the previously
added module-level helpers duplicated TextStepper's line-ending logic and
exposed raw offsets as a low-level data structure shared between two
functions, violating the project's software design principles (each
concern in exactly one home; dataclasses instead of tuples for simple
data storage).

Introduce in solidlsp/ls_utils.py:

- LineCol: frozen, kw-only dataclass for a 0-based line/column position
- TextCoordinates: encapsulates the cached table of line start offsets,
  built via TextStepper (step_line + line_start_idx), with a single
  public method line_col_at_index() resolving an index via binary
  search, including the CRLF rule (an index pointing at the '\n' of a
  '\r\n' pair denotes the beginning of the next line, column 0) and
  InvalidTextLocationError for out-of-range indices

search_text now instantiates TextCoordinates once per file and resolves
each match's coordinates through the public method; the private helpers
(_compute_line_starts, _line_col_at_index) are removed.

Equivalence with TextUtils.get_line_col_from_index verified across
mixed line endings, empty content and boundary indices (0 mismatches).

Tests are behaviour-anchored: the implementation-coupled parametrized
test importing the private helpers is replaced by public-contract tests
of TextCoordinates (test/solidlsp/test_ls_utils.py) and absolute line
assertions through the public search_text API. The benchmark script
uses the public API as well.

Benchmark (synthetic 12k lines, ~723 matches, best of 5): coordinate
resolution ~1764 ms -> ~2 ms; precompute ~1.1 ms; small files unchanged.

Semantics are unchanged; results are identical to the previously
proposed implementation and to the upstream reference implementation.

* fix(test): rename test_ls_utils to test_text_coordinates to avoid basename collision

The new test file collided with the pre-existing upstream
test/solidlsp/util/test_ls_utils.py: pytest (prepend import mode, no
__init__.py in the test dirs) requires unique basenames, and collecting
both modules produced an import-file-mismatch error that aborted
collection with exit code 2 across every CI matrix job.

Rename to test_text_coordinates.py (unique, and matches the class under
test). Full-suite collection verified locally (2252 tests, 0 errors).

test/solidlsp/test_text_coordinates.py

@@ -0,0 +1,101 @@
+import pytest
+
+from solidlsp.ls_utils import InvalidTextLocationError, LineCol, TextCoordinates
+
+
+class TestTextCoordinates:
+    """Tests for the public contract of TextCoordinates and LineCol."""
+
+    @pytest.mark.parametrize(
+        "content",
+        [
+            "hello\nworld\n",
+            "hello\r\nworld\r\n",
+            "hello\rworld\r",
+            "a\rb\nc\r\nd\r\n",
+            "",
+            "no newline at end",
+            "\n",
+            "\r",
+            "a\r\n\r\nb",
+        ],
+    )
+    def test_line_col_at_index_end_to_end(self, content):
+        """Every index within the text resolves to a position that is consistent with the line layout."""
+        coordinates = TextCoordinates(content)
+        for index in range(len(content) + 1):
+            loc = coordinates.line_col_at_index(index)
+            assert loc.line >= 0
+            assert loc.col >= 0
+            # a col greater than 0 implies that none of the col characters before the index is a line separator
+            if loc.col > 0:
+                preceding = content[index - loc.col : index]
+                assert "\n" not in preceding and "\r" not in preceding
+
+    def test_line_col_at_index_basic_lf(self):
+        """Coordinates for LF-only content match the manually derived line layout."""
+        coordinates = TextCoordinates("alpha\nbeta\ngamma\n")
+        assert coordinates.line_col_at_index(0) == LineCol(line=0, col=0)
+        assert coordinates.line_col_at_index(3) == LineCol(line=0, col=3)
+        assert coordinates.line_col_at_index(5) == LineCol(line=0, col=5)
+        assert coordinates.line_col_at_index(6) == LineCol(line=1, col=0)
+        assert coordinates.line_col_at_index(8) == LineCol(line=1, col=2)
+        assert coordinates.line_col_at_index(11) == LineCol(line=2, col=0)
+        assert coordinates.line_col_at_index(12) == LineCol(line=2, col=1)
+        assert coordinates.line_col_at_index(16) == LineCol(line=2, col=5)
+        # an index at the end of the text (after the trailing newline) denotes the start of a new line
+        assert coordinates.line_col_at_index(17) == LineCol(line=3, col=0)
+
+    def test_line_col_at_index_crlf(self):
+        r"""CRLF sequences count as a single line ending. An index pointing at the "\n" of a pair denotes
+        the beginning of the following line (column 0), whereas the "\r" itself still belongs to the
+        preceding line.
+        """
+        coordinates = TextCoordinates("alpha\r\nbeta\r\n")
+        assert coordinates.line_col_at_index(0) == LineCol(line=0, col=0)
+        assert coordinates.line_col_at_index(5) == LineCol(line=0, col=5)
+        assert coordinates.line_col_at_index(6) == LineCol(line=1, col=0)
+        assert coordinates.line_col_at_index(7) == LineCol(line=1, col=0)
+        assert coordinates.line_col_at_index(8) == LineCol(line=1, col=1)
+        assert coordinates.line_col_at_index(11) == LineCol(line=1, col=4)
+        assert coordinates.line_col_at_index(12) == LineCol(line=2, col=0)
+        assert coordinates.line_col_at_index(13) == LineCol(line=2, col=0)
+
+    def test_line_col_at_index_bare_cr(self):
+        r"""Bare "\r" characters act as line separators."""
+        coordinates = TextCoordinates("alpha\rbeta\r")
+        assert coordinates.line_col_at_index(5) == LineCol(line=0, col=5)
+        assert coordinates.line_col_at_index(6) == LineCol(line=1, col=0)
+        assert coordinates.line_col_at_index(10) == LineCol(line=1, col=4)
+        assert coordinates.line_col_at_index(11) == LineCol(line=2, col=0)
+
+    def test_line_col_at_index_mixed(self):
+        """Mixed line endings resolve consistently in a single text."""
+        coordinates = TextCoordinates("a\r\nb\rc\nd\r\n")
+        # "\r\n" ends line 0; "\r" ends line 1; "\n" ends line 2; "\r\n" ends line 3
+        assert coordinates.line_col_at_index(0) == LineCol(line=0, col=0)
+        assert coordinates.line_col_at_index(1) == LineCol(line=0, col=1)
+        assert coordinates.line_col_at_index(2) == LineCol(line=1, col=0)
+        assert coordinates.line_col_at_index(3) == LineCol(line=1, col=0)
+        assert coordinates.line_col_at_index(4) == LineCol(line=1, col=1)
+        assert coordinates.line_col_at_index(5) == LineCol(line=2, col=0)
+        assert coordinates.line_col_at_index(6) == LineCol(line=2, col=1)
+        assert coordinates.line_col_at_index(7) == LineCol(line=3, col=0)
+        assert coordinates.line_col_at_index(8) == LineCol(line=3, col=1)
+        assert coordinates.line_col_at_index(9) == LineCol(line=4, col=0)
+        assert coordinates.line_col_at_index(10) == LineCol(line=4, col=0)
+
+    def test_line_col_at_index_empty_content(self):
+        """The only valid index in empty content resolves to the origin."""
+        coordinates = TextCoordinates("")
+        assert coordinates.line_col_at_index(0) == LineCol(line=0, col=0)
+        with pytest.raises(InvalidTextLocationError):
+            coordinates.line_col_at_index(1)
+
+    def test_line_col_at_index_out_of_range(self):
+        """Indices beyond the text length are rejected."""
+        coordinates = TextCoordinates("abc")
+        with pytest.raises(InvalidTextLocationError):
+            coordinates.line_col_at_index(4)
+        with pytest.raises(InvalidTextLocationError):
+            coordinates.line_col_at_index(-1)