[Draft] page orientation improvements

[felixdittrich92]

This PR:

• refactor OCRPredictor logic (limit duplication)
• extend estimate angle function to handle also upside-down images
• correct return value from estimate angle (negative - left side rot / positive - right side rot) -> update tests
• integrate page_orientation_predictor

NOTE: Draft until TF orientation models are merged

Any feedback is welcome 🤗

Closes: #1460

[codecov]

Codecov Report

Attention: Patch coverage is 98.33333% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 96.29%. Comparing base (9c92f5c) to head (3f93c5e).

Files	Patch %	Lines
doctr/models/_utils.py	95.23%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1553      +/-   ##
==========================================
+ Coverage   96.25%   96.29%   +0.04%     
==========================================
  Files         163      163              
  Lines        7707     7729      +22     
==========================================
+ Hits         7418     7443      +25     
+ Misses        289      286       -3     

Flag	Coverage Δ
unittests	96.29% <98.33%> (+0.04%)	⬆️

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