Pin test tool versions

[gkreitz]

Apparently, ruff 0.16 adds a lot of new checks by default. This caused CI to fail for our latest PR.

This PR pins versions of our dev tools (and pins ruff to 0.15.22 so we can slowly start going through the fixes required for 0.16). I also did some additional QoL fixes:

• Run CI on python 3.14 (the default version in Ubuntu 26.04)
• Add a script ./run_tests.sh to easily run all tests locally. Or make test if you prefer make.
• Add a script to ensure the pinned ruff version stays in sync with the ruff version in our pre-commit-config
• Remove some copy-paste in pyproject.toml - read requirements as a dynamic property

I intentionally decided not to pin the libraries we depend on. I think it's good if CI pulls in the latest pip versions and blows up if upstream changes.

Fixes #331