Support `uv.lock` files out-of-the-box.

`release-please` already understands and correctly manages the `pyproject.toml` file used by [`uv`](https://docs.astral.sh/uv/), but not the`uv.lock` lockfile, which also contains the package version. The trick is to add a special `extra-files` entry to `release-please-config.json`:

```json
"extra-files": [
{
"path": "uv.lock",
"type": "toml",
"jsonpath": "$.package[?(@.name.value=='my-package')].version"
},
```
as described in [this extremely helpful issue comment](https://github.com/googleapis/release-please/issues/2455#issuecomment-2643132770) from a user.

It would be great to not need this trick!