Replace validate_stubs scripts with stubtest

[Avasam]

validate_stubs.py doesn't really work in its current state. I'm sure there's plenty more issues, but mainly it tries to import stub files and stubs-only symbols.

Stubtest is as actively maintained as mypy and is a core tool to typeshed's own testing to validate that stubs match the content of implementation.
https://mypy.readthedocs.io/en/stable/stubtest.html

• Updated .github/workflows/test.yml to test both oldest and newest python version. This will help uncover issues like numpy.distutils not being available on Python 3.12+
  • Done in Test types across environments #375 instead
• In testing dependency group, explicitly install the libraries we're stubbing. This is helpful to quickly see the implementation using Pylance. And required for stubtest.
• All found discrepancy between current stubs and runtime have been added to an allowlist
• Issues that couldn't be ignored have been resolved
• Removed utils/validate_stubs.py in favor of tests/run_stubtest.py

Whilst all other tools help you ensure your stubs are valid, sane, or simply follow modern standards. This is actually the best metric you'll have to see how close the stubs are to actual implementation (or rather, how much they've diverged over time)

[Avasam]

@debonte If you prefer, I can split off the changes to test across different Python versions

[debonte]

@debonte If you prefer, I can split off the changes to test across different Python versions

@Avasam, I don't have a preference. If it makes things easier for you feel free, but I'm ok with the PR as is.

[Avasam]

I think I'm through all the issues anyway ^^
And I had to fix some of these locally either way since I'm running on a Python 3.13 .venv

[Avasam]

As this PR grows, I ended up splitting it off after all: #375