Raise if mx < k. Handle mx = k separately.

[mlondschien]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 2 lines in your changes missing coverage. Please review.

Project coverage is 94.79%. Comparing base (4e27ae5) to head (ddd3a26).
Report is 1 commits behind head on main.

Files	Patch %	Lines
ivmodels/models/kclass.py	83.33%	1 Missing ⚠️
ivmodels/tests/likelihood_ratio.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #113      +/-   ##
==========================================
- Coverage   94.85%   94.79%   -0.07%     
==========================================
  Files          37       37              
  Lines        2313     2323      +10     
==========================================
+ Hits         2194     2202       +8     
- Misses        119      121       +2     

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