Remove transparent link annots from pdfdoc

[kbengs]

Third case in #341 seems to be caused by link annotations in the pdf.
The links are square boxes which link to something. The box can have a visible border but often it is transparent (invisible).
This commit removes the link annotation (box) if it is transparent.

For the pdfs which have transparent links that I have tested this commit with, it does:

• Lower memory usage by 50-100Mb
• Slow down rendering by 2-3% first time a pdf is rendered

The improvement can be seen on this file:
https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/pdf_reference_archives/PDFReference.pdf

We could of course just close # 341 and just live with the issue.

[codecov-commenter]

Codecov Report

Merging #551 (86849b7) into main (960e340) will increase coverage by 0.01%.
The diff coverage is 76.92%.

@@            Coverage Diff             @@
##             main     #551      +/-   ##
==========================================
+ Coverage   72.35%   72.36%   +0.01%     
==========================================
  Files          10       10              
  Lines        2912     2924      +12     
==========================================
+ Hits         2107     2116       +9     
- Misses        805      808       +3     

Impacted Files	Coverage Δ
pdfarranger/core.py	87.29% <76.92%> (-0.43%)	⬇️

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