chore: use cls for classmethods

[dlech]

Replace uses of klass with the expected cls in the one and only classmethod definition.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.24%. Comparing base (ecf5f45) to head (84f8e17).
⚠️ Report is 36 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #545      +/-   ##
==========================================
+ Coverage   85.18%   85.24%   +0.05%     
==========================================
  Files          28       28              
  Lines        3416     3416              
  Branches      600      600              
==========================================
+ Hits         2910     2912       +2     
+ Misses        313      312       -1     
+ Partials      193      192       -1     

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[codspeed-hq]

CodSpeed Performance Report

Merging #545 will not alter performance

_{Comparing use-cls (84f8e17) with main (ecf5f45)}

Summary

✅ 6 untouched