ENH: Add PDF/A XMP metadata support

[Arya-A-Nair]

Closes #3313

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.71%. Comparing base (67d1ba1) to head (c77696b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3314   +/-   ##
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  Coverage   96.71%   96.71%           
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  Files          53       53           
  Lines        9029     9034    +5     
  Branches     1674     1674           
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+ Hits         8732     8737    +5     
  Misses        177      177           
  Partials      120      120           

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[stefan6419846]

Thanks for the PR. I have added some inline remarks.

Additionally, I would like to request some changes/simplifications of the tests:

• The tests should go into test_xmp.py. While the functionality is related to PDF/A, it is just another XMP feature.

• It should be sufficient to have exactly two tests:

  • One with sample-files/021-pdfa/crazyones-pdfa.pdf which has these values.
  • One with sample-files/020-xmp/output_with_metadata_pymupdf.pdf which does not have these values.

  The good thing about these files is that they are already cloned with a proper local development copy of the repository and do not require further downloads (and do not rely on other tests already having downloaded them).

  I suggest to have a look at the other tests utilizing SAMPLE_ROOT as well.