refactor: Refactored holocron.trainer

[frgfm]

This PR introduces the following modifications:

• raises a ValueError in check_setup when the loss becomes infinite or NaN
• split implementations of Trainer by task

[codecov]

Codecov Report

Merging #173 (b36feb0) into master (f7c50eb) will increase coverage by 0.00%.
The diff coverage is 91.52%.

@@           Coverage Diff           @@
##           master     #173   +/-   ##
=======================================
  Coverage   93.82%   93.82%           
=======================================
  Files          51       54    +3     
  Lines        2994     3012   +18     
=======================================
+ Hits         2809     2826   +17     
- Misses        185      186    +1     

Impacted Files	Coverage Δ
holocron/trainer/core.py	90.25% <80.00%> (-0.58%)	⬇️
holocron/trainer/detection.py	88.15% <88.15%> (ø)
holocron/trainer/classification.py	91.07% <91.07%> (ø)
holocron/trainer/__init__.py	100.00% <100.00%> (ø)
holocron/trainer/segmentation.py	100.00% <100.00%> (ø)