Removed Python 3.9 support

[StokesMIDE]

• Removed Python 3.9 from the classifiers
• Changed Sphinx workflow to use Python 3.13
• Removed some overly cautious warnings-as-failures from unit tests

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.36%. Comparing base (fbb45a5) to head (f72af82).
⚠️ Report is 1 commits behind head on development.

Additional details and impacted files

@@             Coverage Diff              @@
##           development     #241   +/-   ##
============================================
  Coverage        71.36%   71.36%           
============================================
  Files               35       35           
  Lines             3279     3279           
============================================
  Hits              2340     2340           
  Misses             939      939           

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