feat: add rboxes rectification in Linknet postprocessing

[charlesmindee]

This PR is an update of the linknet postprocessor, so that it is similar to the DB.

Any feedback is welcome!

[fg-mindee]

Looks good! Would you mind adding a small docstring for this method on both the DBNet & LinkNet to explain a bit the usage of those new args please?

[fg-mindee]

Small typos to fix 🙏

[fg-mindee]

Cheers 🙏

[codecov]

Codecov Report

Merging #679 (2d52e46) into main (8382896) will increase coverage by 0.01%.
The diff coverage is 68.42%.

@@            Coverage Diff             @@
##             main     #679      +/-   ##
==========================================
+ Coverage   96.28%   96.29%   +0.01%     
==========================================
  Files         117      117              
  Lines        4523     4538      +15     
==========================================
+ Hits         4355     4370      +15     
  Misses        168      168              

Flag	Coverage Δ
unittests	96.29% <68.42%> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
...dels/detection/differentiable_binarization/base.py	92.77% <ø> (+2.77%)	⬆️
doctr/models/detection/linknet/base.py	85.14% <68.42%> (-3.88%)	⬇️
doctr/utils/geometry.py	98.00% <0.00%> (ø)
doctr/datasets/sroie.py	97.14% <0.00%> (+2.27%)	⬆️

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