Allow Python 3.13 and Astropy 7.x

[teutoburg]

Test green locally on Windows using Python 3.13.

This has no internal dependencies, so can be merged already.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.01%. Comparing base (dafe9af) to head (12a0ee9).
⚠️ Report is 35 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #38   +/-   ##
=======================================
  Coverage   97.01%   97.01%           
=======================================
  Files           3        3           
  Lines          67       67           
=======================================
  Hits           65       65           
  Misses          2        2           

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