Turn the fuzz-parser script into a properly packaged Python project

[AlexWaygood]

Summary

This PR gets rid of the requirements.in and requirements.txt files in the scripts/fuzz-parser directory, and replaces them with pyproject.toml and uv.lock files. The script is renamed from fuzz-parser to py-fuzzer (since it can now also be used to fuzz red-knot as well as the parser, following #14566), and moved from the scripts/ directory to the python/ directory, since it's now a (uv)-pip-installable project in its own right.

I've been resisting this for a while, because conceptually this script just doesn't feel "complicated" enough to me for it to be a full-blown package. However, I think it's time to do this. Making it a proper package has several advantages:

• It means we can run it from the project root using uv run without having to activate a virtual environment and ensure that all required dependencies are installed into that environment
• Using a pyproject.toml file means that we can express that the project requires Python 3.12+ to run properly; this wasn't possible before
• I've been running mypy on the project locally when I've been working on it or reviewing other people's PRs; now I can put the mypy config for the project in the pyproject.toml file

Test Plan

I manually tested that all the commands detailed in python/py-fuzzer/README.md work for me locally.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

Formatter (stable)

✅ ecosystem check detected no format changes.

Formatter (preview)

✅ ecosystem check detected no format changes.

[sharkdp]

Thanks!

[MichaReiser]

I like it :)