chore(deps): anthropic 1.5, openai 3.13, and the move to httpx2

Both SDKs' 1.x/3.x majors run on httpx2 (the maintained fork of httpx by its
original author, published by Pydantic at github.com/pydantic/httpx2, version
line 2.x) instead of httpx, which is what makes these two bumps one change.
httpx2 is now a declared dependency because two modules import it directly.
Everything else in the 0.x -> 1.x / 2.x -> 3.x change lists is absent here:
no Text Completions, no `with_raw_response`, no raw `output_format` dicts, no
Bedrock client, and `requires-python` is already 3.12.

Three code changes, all forced by the bump:

The BYOM DNS-pinning client in `docsgpt/security/safe_url.py` is handed to
`OpenAI(http_client=...)`, and the SDK rejects an old-httpx client at
construction — which would have taken the SSRF guard offline. It is built on
httpx2 now, and its `sni_hostname` extension carries a `str` rather than
ascii bytes: httpcore passes the value straight to
`ssl.SSLContext.wrap_socket`, and the truststore backend httpx2 uses for the
default system trust store encodes it instead of accepting bytes. Bytes
therefore failed every real handshake while passing the existing tests, which
stub the transport out; the test now pins the type and says why.

The stream-retry error tuple in `docsgpt/llm/base.py` named `httpx`
exceptions only. The two libraries' exception classes are unrelated types, so
after the bump the retry silently stopped firing for openai and anthropic
while still working for google-genai and elevenlabs. It now covers both
stacks, with a parametrized test over each.

anthropic 1.x dropped temperature/top_p/top_k from `messages.create`'s
signature (passing one raises TypeError) without dropping them from the API,
so the provider forwards them through `extra_body`. The wire request is
unchanged and a model that rejects them 400s exactly as before.

tests/security/test_safe_url.py

@@ -537,7 +537,7 @@ def _capture_httpx_handle_request(monkeypatch):
     opening a real socket.
     """
 
-    import httpx
+    import httpx2
 
     captured: dict = {}
 
@@ -545,10 +545,10 @@ def _capture_httpx_handle_request(monkeypatch):
         captured["url"] = request.url
         captured["sni"] = request.extensions.get("sni_hostname")
         captured["host_header"] = request.headers.get("host")
-        return httpx.Response(200, content=b"ok")
+        return httpx2.Response(200, content=b"ok")
 
     monkeypatch.setattr(
-        "httpx.HTTPTransport.handle_request", fake_handle
+        "httpx2.HTTPTransport.handle_request", fake_handle
     )
     return captured
 
@@ -610,7 +610,14 @@ def test_pinned_httpx_transport_rewrites_url_to_validated_ip(monkeypatch):
 def test_pinned_httpx_transport_sets_sni_for_original_hostname(monkeypatch):
     """TLS SNI / cert verification must use the original hostname; the
     transport sets it via the ``sni_hostname`` extension that
-    httpcore forwards to ``start_tls``'s ``server_hostname``."""
+    httpcore forwards to ``start_tls``'s ``server_hostname``.
+
+    The value must be a ``str``, not ascii bytes: httpcore passes it
+    straight to ``ssl.SSLContext.wrap_socket``, and the ``truststore``
+    backend httpx2 uses for the default system trust store encodes it
+    rather than accepting bytes — so bytes fail every real handshake
+    while passing any test that stubs the transport out.
+    """
 
     captured = _capture_httpx_handle_request(monkeypatch)
 
@@ -623,7 +630,8 @@ def test_pinned_httpx_transport_sets_sni_for_original_hostname(monkeypatch):
     finally:
         client.close()
 
-    assert captured["sni"] == b"api.example.com"
+    assert captured["sni"] == "api.example.com"
+    assert isinstance(captured["sni"], str)
 
 
 @pytest.mark.unit
@@ -712,7 +720,7 @@ def test_pinned_httpx_transport_refuses_unexpected_host(monkeypatch):
     transport refuses rather than silently dialing the validated IP
     with a different host's credentials."""
 
-    import httpx
+    import httpx2
 
     with mock.patch(
         "socket.getaddrinfo", return_value=_addrinfo("104.18.6.192")
@@ -721,7 +729,7 @@ def test_pinned_httpx_transport_refuses_unexpected_host(monkeypatch):
     try:
         with pytest.raises(UnsafeUserUrlError, match="refused request"):
             client.get("https://other.example.com/v1/test")
-    except httpx.RequestError:
+    except httpx2.RequestError:
         # Some httpx versions may wrap the transport error; accept
         # either path so long as the request didn't succeed.
         pass