## Summary
This PR adds support for VS Code specific cell metadata to consider when
collecting valid code cells.
For context, Ruff only runs on valid code cells. These are the code
cells that doesn't contain cell magics. Previously, Ruff only used the
notebook's metadata to determine whether it's a Python notebook. But, in
VS Code, a notebook's preferred language might be Python but it could
still contain code cells for other languages. This can be determined
with the `metadata.vscode.languageId` field.
### References:
* https://code.visualstudio.com/docs/languages/identifiers
* e6c009a3d4/extensions/ipynb/src/serializers.ts (L104-L107)
*
e6c009a3d4/extensions/ipynb/src/serializers.ts (L117-L122)
This brings us one step closer to fixing #12281.
## Test Plan
Add test cases for `is_valid_python_code_cell` and an integration test
case which showcase running it end to end. The test notebook contains a
JavaScript code cell and a Python code cell.
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