Introduce DownloadedDependency abstraction with URL-keyed hash database

* Add DownloadedDependency abstraction to facilitate handling of downloaded
  and hash-verified dependencies.
  In CI, missing hashes raise an exception.
  For users, unverified downloads log a warning.
* Add DownloadedDependencyHashDatabase which manages a URL-keyed database
  of sha256 hashes. It can be conveniently updated incrementally through a
  script (src/solidlsp/resources/downloaded_dependency_hashes.json),
  provided that language server implementations provide DownloadedDependency
  instances statically

Applied in EclipseJDTLS:
* Replace the untyped nested-dict runtime dependency descriptors with DownloadedDependency instances
* Move the JDTLS version-pinning constants into DependencyProvider
* Replace the platform dependency dicts with the VSCodeJavaConfig dataclass

Utils:
 * Add FileUtils.ArchiveType to type archive types that were previously plain str
 * Add is_running_in_ci() to ls_utils

Updated memory on adding a language server accordingly.

test/solidlsp/java/test_jdtls_path_resolution.py

@@ -545,9 +545,7 @@ class TestComputeWorkspaceHash:
     UPSTREAM_LAUNCHER = "/opt/homebrew/Cellar/jdtls/1.50.0/libexec/plugins/org.eclipse.equinox.launcher_1.7.0.jar"
 
     def _initial_settings(self) -> "SolidLSPSettings.CustomLSSettings":
-        from solidlsp.language_servers.eclipse_jdtls import INITIAL_VSCODE_JAVA_VERSION
-
-        return SolidLSPSettings.CustomLSSettings({"vscode_java_version": INITIAL_VSCODE_JAVA_VERSION})
+        return SolidLSPSettings.CustomLSSettings({"vscode_java_version": EclipseJDTLS.DependencyProvider.INITIAL_VSCODE_JAVA_VERSION})
 
     def test_initial_default_mode_matches_pre_upstream_format(self) -> None:
         """Legacy carve-out: INITIAL default-mode hash MUST equal md5(repository_root_path)."""