Learning rate scheduler can be checkpointed now

[georgeyiasemis]

HasStateDict type changed to include torch.optim.lr_scheduler._LRScheduler which was missing before, causing the checkpointer to not save/load the state_dict of LRSchedulers.

[codecov]

Codecov Report

Merging #218 (aab2e3e) into main (702b8f4) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #218      +/-   ##
==========================================
- Coverage   81.28%   81.26%   -0.02%     
==========================================
  Files          73       73              
  Lines        5433     5433              
==========================================
- Hits         4416     4415       -1     
- Misses       1017     1018       +1     

Impacted Files	Coverage Δ
direct/nn/openvino/openvino_model.py	97.18% <100.00%> (ø)
direct/types.py	100.00% <100.00%> (ø)
direct/checkpointer.py	71.42% <0.00%> (-0.80%)	⬇️

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