[metrics] speed up polygon iou (for --rotation) by keeping balanced memory footprint

[felixdittrich92]

This PR:

• boost polygon iou (from hours to a few minutes) and try to keep an balanced memory consumption
• remove now unused functions in metrics.py
• remove unused use_broadcasting / mask_shape and psutil requirements for references
• memory usage tested with oversampled funsd validation dataset (~4K samples) tooks around 6.5 GB RAM

Any feedback is welcome 🤗

Closes: #1472

[felixdittrich92]

failing tests: hf hub is down :D

[codecov]

Codecov Report

Attention: Patch coverage is 11.76471% with 15 lines in your changes are missing coverage. Please review.

Project coverage is 57.76%. Comparing base (f21ac32) to head (469e620).

❗ Current head 469e620 differs from pull request most recent head cc81298. Consider uploading reports for the commit cc81298 to get more accurate results

Files	Patch %	Lines
doctr/utils/metrics.py	11.76%	15 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1561      +/-   ##
==========================================
+ Coverage   57.70%   57.76%   +0.05%     
==========================================
  Files         167      166       -1     
  Lines        7696     7624      -72     
==========================================
- Hits         4441     4404      -37     
+ Misses       3255     3220      -35     

Flag	Coverage Δ
unittests	57.76% <11.76%> (+0.05%)	⬆️

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