Not sure how these got missed when moving other things to `uv`, but this
should clean them up.
The bump to Python 3.12 is so that we can use `@override` with the
simple import from `typing`. This is needed by the newest versions of
`ty` to do type checking. Added the relevant `@override` annotations.
Assisted-by: Antigravity with Gemini
This is making it consistent with other places we set a Python version:
- contribution_tools.md
- .python-version
- bench_runner.py
- build-setup-common/action.yml
Assisted-by: Google Antigravity with Gemini