Modernize ci setup

[Zethson]

There's a lot more to be done but this only took me a few minutes.

• Use Ruff format instead of Black
• Use UV for RTD significantly speeding it up
• Remove flake8 and other old things
• Remove preprocessing from the docs (which is what I actually only wanted to do)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.21%. Comparing base (b314b75) to head (96dbd5f).
⚠️ Report is 23 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #434   +/-   ##
=======================================
  Coverage   85.21%   85.21%           
=======================================
  Files           8        8           
  Lines        1759     1759           
=======================================
  Hits         1499     1499           
  Misses        260      260           

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[timtreis]

merci!