Add support for Python 3.13, remove advertised support for Python 3.8

[Viicos]

Bare minimum, so code isn't updated with the 3.8 removal (I can go happily go over it though).

[codecov-commenter]

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@@            Coverage Diff             @@
##             main     #514      +/-   ##
==========================================
- Coverage   96.27%   96.10%   -0.18%     
==========================================
  Files          11       11              
  Lines        1074     1078       +4     
  Branches      209      144      -65     
==========================================
+ Hits         1034     1036       +2     
- Misses         19       21       +2     
  Partials       21       21              

see 1 file with indirect coverage changes

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