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

src/version/types.ts

@@ -4,7 +4,7 @@ export type VersionSource =
   | "pyproject.toml"
   | "default";
 
-export type VersionFileFormat = "pyproject.toml" | "requirements";
+export type VersionFileFormat = "pyproject.toml" | "requirements" | "uv.lock";
 
 export interface ParsedVersionFile {
   format: VersionFileFormat;