chore: Type constants final and inherit enum

[zhongjiajie]

related from https://peps.python.org/pep-0591/

[codecov-commenter]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (9a28820) 95.65% compared to head (8861369) 95.69%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main      #27      +/-   ##
==========================================
+ Coverage   95.65%   95.69%   +0.04%     
==========================================
  Files           7        7              
  Lines         184      186       +2     
==========================================
+ Hits          176      178       +2     
  Misses          8        8              

Flag	Coverage Δ
unittests	95.69% <100.00%> (+0.04%)	⬆️

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Files	Coverage Δ
src/stmdency/constants.py	100.00% <100.00%> (ø)

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