Add Python 3.13 support, drop 3.9

[greschd]

Closes #139.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.65%. Comparing base (4569d96) to head (35497ed).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #140      +/-   ##
==========================================
- Coverage   89.77%   89.65%   -0.12%     
==========================================
  Files           3        3              
  Lines          88       87       -1     
==========================================
- Hits           79       78       -1     
  Misses          9        9              

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