fix: Added missing AMP flags in training scripts

[fg-mindee]

This PR simply adds the missing AMP flags to enable it on all training & evaluation loops for PyTorch.

Any feedback is welcome!

[codecov]

Codecov Report

Merging #690 (cf94633) into main (9c45ba6) will decrease coverage by 0.36%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #690      +/-   ##
==========================================
- Coverage   96.40%   96.04%   -0.37%     
==========================================
  Files         117      117              
  Lines        4540     4548       +8     
==========================================
- Hits         4377     4368       -9     
- Misses        163      180      +17     

Flag	Coverage Δ
unittests	96.04% <ø> (-0.37%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
doctr/models/recognition/crnn/pytorch.py	94.18% <0.00%> (-5.82%)	⬇️
...dels/detection/differentiable_binarization/base.py	89.44% <0.00%> (-3.34%)	⬇️
doctr/models/recognition/master/pytorch.py	93.47% <0.00%> (-2.11%)	⬇️
doctr/models/detection/linknet/base.py	85.14% <0.00%> (-1.99%)	⬇️
...s/detection/differentiable_binarization/pytorch.py	97.50% <0.00%> (-0.81%)	⬇️
doctr/models/detection/linknet/pytorch.py	98.07% <0.00%> (+0.03%)	⬆️

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[charlesmindee]

Thanks for the PR!