Add free-threading compatibility and drop Python 3.10 support

[djhoese]

Adds necessary flags to Cython extensions to say they are free-threading compatible. Adds Python 3.13 to CI. Adds free-threaded wheel building. Cleans up metadata and config files.

I got pre-approval of these changes on slack from multiple core pytroll devs so I'll merge it when CI passes.

• Closes #xxxx
• Tests added
• Tests passed
• Passes git diff origin/main **/*py | flake8 --diff
• Fully documented

[djhoese]

I'm making GitHub confused because I keep accidentally pushing my branch to the pytroll repos instead of my fork. CI is actually running, github just doesn't show it properly.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.69%. Comparing base (ffc1628) to head (3c33e42).
⚠️ Report is 46 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #102      +/-   ##
==========================================
+ Coverage   88.43%   88.69%   +0.25%     
==========================================
  Files          20       20              
  Lines        1522     1521       -1     
==========================================
+ Hits         1346     1349       +3     
+ Misses        176      172       -4     

Flag	Coverage Δ
unittests	88.69% <ø> (+0.25%)	⬆️

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[coveralls]

coverage: 87.965%. remained the same
when pulling 3c33e42 on djhoese:feat-freethreading
into f00b858 on pytroll:main.

[djhoese]

Ah I need to drop Python 3.10 support if I want to build Windows ARM64 wheels. Numpy 2.2.6 is the last version to support Python 3.10, but doesn't provide Windows ARM64 wheels. Maybe I just turn off Windows ARM64 wheels for now...