Enable free-threading in cython extensions

[djhoese]

Needs to be rebased onto #672 once it is merged to make sure that free-threading wheel builds succeed with these changes.

• Closes #xxxx
• Tests added
• Tests passed
• Fully documented

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.67%. Comparing base (4da28b0) to head (f489766).
⚠️ Report is 11 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #676   +/-   ##
=======================================
  Coverage   93.67%   93.67%           
=======================================
  Files          89       89           
  Lines       13621    13621           
=======================================
  Hits        12759    12759           
  Misses        862      862           

Flag	Coverage Δ
unittests	93.67% <ø> (ø)

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[coveralls]

coverage: 93.709%. remained the same
when pulling f489766 on djhoese:feat-free-threading
into 1f4c7fb on pytroll:main.