Removed custom implementation and using cv2 (BugFix)

[fernando79513]

Description

For some weird reason, when the two images were the same, the tests were failing in later versions of python (3.13), but not in early ones. This was probably due to a rounding error.

# python 3.8
>>> _get_psnr(img1, img2)
1.0686215807909677e-07
# python 3.13
>>> _get_psnr(img1, img2)
0.0

Nevertheless, the implementation of the algorithm was wrong, and it returned 0 instead of a big value if the images were exactly the same.

I've just changed it to use the default one from opencv (cv2.PSNR)

Resolved issues

Documentation

Tests

Tested with python 3.13

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 49.62%. Comparing base (7817ae2) to head (f285420).
Report is 123 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1776      +/-   ##
==========================================
- Coverage   49.63%   49.62%   -0.02%     
==========================================
  Files         377      377              
  Lines       40630    40619      -11     
  Branches     6830     6829       -1     
==========================================
- Hits        20168    20157      -11     
  Misses      19740    19740              
  Partials      722      722              

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