Redefine uv.lock have custom 'uvlock' file type

(Sorry not sure what the right terminology is.)

The main reason to do this is because `ruff` can lint the `uv.lock` file and it uses `types_or` to match files. If `ruff` were to match against 'toml' in its `types_or` it would match too many files. So the idea is to merge this then update ruff's hook definition to

```diff
 - id: ruff-check
   name: ruff check
   description: "Run 'ruff check' for extremely fast Python linting"
   entry: ruff check --force-exclude
   language: python
-  types_or: [python, pyi, jupyter, uvlock]
+  types_or: [python, pyi, jupyter]
```

I got this idea by looking at how jenkinfiles is defined; although it's a groovy file, it has a custom jenkinsfile-specific file type in this extensions file.

Author: mxr

identify/extensions.py

@@ -434,7 +434,7 @@
     'sys.config': EXTENSIONS['erl'],
     'sys.config.src': EXTENSIONS['erl'],
     'Tiltfile': {'text', 'tiltfile'},
-    'uv.lock': EXTENSIONS['toml'],
+    'uv.lock': {'text', 'toml', 'uvlock'},
     'Vagrantfile': EXTENSIONS['rb'],
     'WORKSPACE': EXTENSIONS['bzl'],
     'wscript': EXTENSIONS['py'],