languages: Fix Python LSP workspace folder detection in uv workspaces

[space192]

Closes #47926

Summary

When using a uv (or Poetry/PDM) workspace with multiple subprojects, Python LSP servers (Pyright, Ruff, ty, etc.) are initialized with the subproject directory as their workspace folder instead of the workspace root. This happens because PyprojectTomlManifestProvider::search() returns the first (innermost)
pyproject.toml found walking up the directory tree.

For example, in a uv workspace like:

main-project/
├── pyproject.toml # workspace root with [tool.uv.workspace]
├── uv.lock
├── packages/
│ └── project-api/
│ └── pyproject.toml # subpackage
└── projects/
└── project-a/
└── pyproject.toml # subpackage

Opening a file in packages/project-api/ would register packages/project-api/ as the LSP workspace folder instead of main-project/.

Approach

The fix uses lockfile existence as a heuristic to detect workspace roots. The updated search() method walks all ancestors (similar to CargoManifestProvider) and:

• Tracks the innermost pyproject.toml as a fallback
• Tracks the outermost pyproject.toml that has a sibling lockfile (uv.lock, poetry.lock, pdm.lock, or Pipfile.lock)
• Returns the outermost workspace root if found, otherwise falls back to the innermost

This works within the existing ManifestDelegate interface (existence checks only, no file content reading).

Scenario	Result
uv workspace (root pyproject.toml + uv.lock)	Returns workspace root
Poetry workspace (root pyproject.toml + poetry.lock)	Returns workspace root
Simple project (single pyproject.toml, no lockfile)	Returns project dir (unchanged)
Independent subprojects (no lockfile at any level)	Returns each project's own dir (unchanged)

Since the manifest provider is set at the Python language level, this fix applies to all Python LSP servers (Pyright, Ruff, ty, etc.).

Test plan

• Added unit tests for PyprojectTomlManifestProvider covering all scenarios above
• Existing integration test test_running_multiple_instances_of_a_single_server_in_one_worktree passes (independent subprojects without lockfiles)
• cargo check -p languages compiles cleanly
• Manual testing with a real uv workspace (Pyright and Ruff both receive correct workspace root)

Release Notes:

• Fixed Python LSP servers (Pyright, Ruff, etc.) using the wrong workspace folder in uv/Poetry/PDM workspaces with multiple subprojects.

[osiewicz]

Makes sense to me. Thanks!