feat: support uv.lock as version-file (#379)

Adds `uv.lock` as a supported `version-file` format, alongside the
existing
`pyproject.toml` and `requirements.txt`. A `uv.lock` pins the exact
resolved
ruff version, so reading it gives a reproducible install that matches
the
project's lockfile — the single source of truth — instead of the
lower-bound /
range typically declared in `pyproject.toml`.

The parser reads the `[[package]]` entry whose `name` is `ruff` and
returns its
`version`. If ruff is absent or the file cannot be parsed, the action
warns and
falls back to `latest` (same behaviour as the other formats).

Validation:
- `npm run all` — tsc typecheck clean, biome clean, dist rebuilt, jest
65/65 pass
- Added unit tests (`__tests__/version/file-parser.test.ts`) + a
`uv.lock` fixture
- Added an integration job (`test-default-version-from-uv-lock`) that
runs the
  action against the fixture and asserts ruff 0.9.5 is installed

closes #375

.github/workflows/test.yml

@@ -280,6 +280,25 @@ jobs:
           fi
         env:
           RUFF_VERSION: ${{ steps.ruff-action.outputs.ruff-version }}
+  test-default-version-from-uv-lock:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+      - name: Use default version from uv.lock
+        id: ruff-action
+        uses: ./
+        with:
+          src: __tests__/fixtures/python-project
+          version-file: __tests__/fixtures/uv.lock
+      - name: Correct version gets installed
+        run: |
+          if [ "$RUFF_VERSION" != "0.9.5" ]; then
+            exit 1
+          fi
+        env:
+          RUFF_VERSION: ${{ steps.ruff-action.outputs.ruff-version }}
   test-semver-range:
     runs-on: ubuntu-latest
     steps:
@@ -501,6 +520,7 @@ jobs:
       - test-default-version-from-pyproject-optional-dependencies
       - test-default-version-from-requirements
       - test-default-version-from-requirements-with-hash
+      - test-default-version-from-uv-lock
       - test-semver-range
       - test-pep440-version-specifier
       - test-checksum