Add CUDA tests to the test matrix

[mdekstrand]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.49%. Comparing base (5072a5d) to head (f871317).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lenskit/flexmf/_training.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1188      +/-   ##
==========================================
+ Coverage   90.43%   90.49%   +0.05%     
==========================================
  Files         263      263              
  Lines       17602    17605       +3     
==========================================
+ Hits        15919    15931      +12     
+ Misses       1683     1674       -9     

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