ENHANCEMENT: Handle mono classification with Shap

[degenfabian]

Hi!
This PR intends to address issue #428. For the edge case described in the issue, instead of throwing an error, the program now outputs a warning that the model was only trained on one class and then creates a wrapper model that assigns 1 to said class and 0 to a synthetic class. This way no error is thrown anymore with the example provided in the issue.

[codecov]

Codecov Report

Attention: Patch coverage is 14.28571% with 12 lines in your changes missing coverage. Please review.

Project coverage is 75.71%. Comparing base (0b5034f) to head (a5f1100).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
...n/interpret-core/interpret/utils/_unify_predict.py	14.28%	12 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #582      +/-   ##
===========================================
- Coverage    75.80%   75.71%   -0.10%     
===========================================
  Files           72       72              
  Lines         9081     9095      +14     
===========================================
+ Hits          6884     6886       +2     
- Misses        2197     2209      +12     

Flag	Coverage Δ
bdist_linux_310_python	75.38% <14.28%> (-0.10%)	⬇️
bdist_linux_311_python	75.28% <14.28%> (-0.22%)	⬇️
bdist_linux_312_python	75.38% <14.28%> (-0.10%)	⬇️
bdist_linux_39_python	75.14% <14.28%> (-0.31%)	⬇️
bdist_mac_310_python	75.55% <14.28%> (-0.10%)	⬇️
bdist_mac_311_python	75.55% <14.28%> (-0.12%)	⬇️
bdist_mac_312_python	75.45% <14.28%> (-0.20%)	⬇️
bdist_mac_39_python	75.43% <14.28%> (-0.22%)	⬇️
bdist_win_310_python	75.49% <14.28%> (-0.20%)	⬇️
bdist_win_311_python	75.39% <14.28%> (-0.30%)	⬇️
bdist_win_312_python	75.56% <14.28%> (-0.12%)	⬇️
bdist_win_39_python	75.47% <14.28%> (-0.18%)	⬇️
sdist_linux_310_python	75.29% <14.28%> (-0.12%)	⬇️
sdist_linux_311_python	75.12% <14.28%> (-0.26%)	⬇️
sdist_linux_312_python	75.12% <14.28%> (-0.29%)	⬇️
sdist_linux_39_python	75.26% <14.28%> (-0.14%)	⬇️
sdist_mac_310_python	75.40% <14.28%> (-0.08%)	⬇️
sdist_mac_311_python	75.38% <14.28%> (-0.22%)	⬇️
sdist_mac_312_python	75.45% <14.28%> (-0.12%)	⬇️
sdist_mac_39_python	75.35% <14.28%> (-0.20%)	⬇️
sdist_win_310_python	75.56% <14.28%> (-0.10%)	⬇️
sdist_win_311_python	75.49% <14.28%> (-0.22%)	⬇️
sdist_win_312_python	75.51% <14.28%> (-0.18%)	⬇️
sdist_win_39_python	75.44% <14.28%> (-0.19%)	⬇️

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[paulbkoch]

Thanks for the fix @degenfabian! Nice to clear this one out too!