fix: Fixed deprecation warnings from numpy & PyMuPDF

[fg-mindee]

This PR fixes the multiple deprecation warnings from PyMuPDF & numpy by using the recommended replacement.

Any feedback is welcome!

[charlesmindee]

Thanks!

[codecov]

Codecov Report

Merging #692 (6d3263b) into main (050faf1) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #692      +/-   ##
==========================================
+ Coverage   95.99%   96.08%   +0.08%     
==========================================
  Files         117      117              
  Lines        4548     4548              
==========================================
+ Hits         4366     4370       +4     
+ Misses        182      178       -4     

Flag	Coverage Δ
unittests	96.08% <100.00%> (+0.08%)	⬆️

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Impacted Files	Coverage Δ
doctr/datasets/doc_artefacts.py	94.11% <100.00%> (ø)
doctr/io/pdf.py	100.00% <100.00%> (ø)
doctr/models/_utils.py	95.34% <100.00%> (ø)
doctr/utils/metrics.py	97.40% <100.00%> (ø)
doctr/models/detection/linknet/base.py	85.14% <0.00%> (+1.98%)	⬆️
doctr/models/recognition/predictor/pytorch.py	96.96% <0.00%> (+6.06%)	⬆️

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