maintenance: add python 3.12 compatibility, uv, dependencies

[mikapfl]

Pull request

Please confirm that this pull request has done the following:

• Tests added
• Documentation added (where applicable)
• Description in a .rst file in the directory changelog_unreleased added - remember to include a * to make it a bullet point

Description

• Add python 3.12 compatibility - closes: Unit handling in xarray fails for Python 3.12 #205 closes: Python 3.12 compatibility #255
  This only needed updates in our dependencies, so easy to do.
• Tighten dependencies - we now have minimum supported versions for all dependencies.
• Add testing with the lowest supported versions to github action workflows
• Use uv pip instead of pip everywhere, it is faster
• optimize github actions for more caching

[mikapfl]

This was surprisingly easy to do, until I started testing on Windows, then it was surprisingly hard to do.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.00%. Comparing base (1f0ccc3) to head (782d258).
Report is 16 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #259      +/-   ##
==========================================
+ Coverage   96.97%   97.00%   +0.02%     
==========================================
  Files          45       45              
  Lines        4336     4336              
==========================================
+ Hits         4205     4206       +1     
+ Misses        131      130       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[mikapfl]

We now do caching via uv and it works quite well. This is also more important now that we have a larger test matrix, which also involves somewhat unusual combinations of older library versions on newer python versions. These need to be compiled often because binary wheel are not available, which takes quite long, but is nicely cached by uv.

[mikapfl]

I also re-enabled xdoctests, they were relatively easy to fix and are useful after all.