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

action.yml

@@ -15,7 +15,7 @@ inputs:
     required: false
     default: ""
   version-file:
-    description: "Path to a pyproject.toml or requirements.txt file to read the version from. If parsing fails, the action warns and falls back to `latest`."
+    description: "Path to a pyproject.toml, requirements.txt or uv.lock file to read the version from. If parsing fails, the action warns and falls back to `latest`."
     required: false
   checksum:
     description: "The checksum of the ruff version to install"