chore: Test Python 3.14 support

[effigies]

Builds on #988. I expect failure, but maybe we'll be lucky.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.20%. Comparing base (a162ad1) to head (85986d0).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #989   +/-   ##
=======================================
  Coverage   71.20%   71.20%           
=======================================
  Files          89       89           
  Lines        8578     8578           
  Branches      931      931           
=======================================
  Hits         6108     6108           
  Misses       2238     2238           
  Partials      232      232           

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