Bugfixes and improvements to protopipe-MODELS

[HealthyPear]

This PR fixes some bugs uncovered by fixing the associated integration test (PR #120)

[codecov]

Codecov Report

Merging #122 (9198cec) into master (0dc958c) will decrease coverage by 0.02%.
The diff coverage is 22.22%.

@@            Coverage Diff             @@
##           master     #122      +/-   ##
==========================================
- Coverage   47.64%   47.61%   -0.03%     
==========================================
  Files          22       22              
  Lines        1992     1995       +3     
==========================================
+ Hits          949      950       +1     
- Misses       1043     1045       +2     

Impacted Files	Coverage Δ
protopipe/mva/train_model.py	60.78% <0.00%> (ø)
protopipe/scripts/build_model.py	60.62% <25.00%> (-0.67%)	⬇️

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