feat: add preserve aspect ratio to predictor and vizualisation utils

[charlesmindee]

This PR allows to use the preserve_aspect_ratio flag in the predictor:

model = ocr_predictor(pretrained=True, assume_straight_pages=False, preserve_aspect_ratio=True)
doc = DocumentFile.from_images(path)
result = model(doc)
result.show(doc, preserve_aspect_ratio=True)

Yields:

Instead of:

Any feedback is welcome!

[fg-mindee]

Thanks, a few improvement suggestions in the review!

[codecov]

Codecov Report

Merging #766 (2c333ae) into main (f2f1f21) will decrease coverage by 0.06%.
The diff coverage is 40.00%.

@@            Coverage Diff             @@
##             main     #766      +/-   ##
==========================================
- Coverage   96.19%   96.13%   -0.07%     
==========================================
  Files         129      129              
  Lines        4810     4812       +2     
==========================================
- Hits         4627     4626       -1     
- Misses        183      186       +3     

Flag	Coverage Δ
unittests	96.13% <40.00%> (-0.07%)	⬇️

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

Impacted Files	Coverage Δ
doctr/models/zoo.py	100.00% <ø> (ø)
doctr/utils/visualization.py	90.26% <25.00%> (-0.73%)	⬇️
doctr/io/elements.py	92.09% <100.00%> (ø)
doctr/models/recognition/predictor/tensorflow.py	91.17% <0.00%> (-5.89%)	⬇️

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[fg-mindee]

Thanks again!