build: drop python3.8 add python 3.13

[tlambert03]

also closes #119

[codspeed-hq]

CodSpeed Performance Report

Merging #121 will not alter performance

_{Comparing tlambert03:py313 (1b5ee5e) with main (1ed5f44)}

Summary

✅ 5 untouched benchmarks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (1ed5f44) to head (1b5ee5e).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #121   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            5         5           
  Lines          522       519    -3     
=========================================
- Hits           522       519    -3     

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