fix: Fixed Mixup for binary & one-hot targets

[frgfm]

This PR introduces the following modifications:

• fixes the arg passing of the mixup alpha to the training script
• fixes support for one-hot and binary targets
• extends unittests

[codecov]

Codecov Report

Merging #225 (622dcf7) into main (89e8aee) will increase coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 622dcf7 differs from pull request most recent head eb8ad82. Consider uploading reports for the commit eb8ad82 to get more accurate results

@@            Coverage Diff             @@
##             main     #225      +/-   ##
==========================================
+ Coverage   93.50%   93.51%   +0.01%     
==========================================
  Files          56       56              
  Lines        3127     3132       +5     
==========================================
+ Hits         2924     2929       +5     
  Misses        203      203              

Impacted Files	Coverage Δ
holocron/utils/data/collate.py	100.00% <100.00%> (ø)