Add full equivalence between different types of linebreaks

[tacc-tacc]

Goal: to consider the three linebreaks (\n, \r, and \r\n) all the same while reading/paarsing wikitext.
Changes made:

• On regex patterns, changed all occurences of \n and \r\n for \R, and [^\n...] replaced with [^\r\n...]
• On regex patterns, replace all ^ and $ anchor/boundary tokens with (?<=\R|\A) and (?=\R\Z), respectively, when talinkg about multiline modes. On non multiline modes, just replace them with \A and \Z for better readability.
• Remove MULTILINE FLAG since we don't need it anymore
• On _table.py, added a new regex pattern to search for the first occurence of a linebreak (\R). I suggest to review further this file since I changed some lines of the logic/flow to adress multi-valued and variable-lengthed linebreaks, but I think it didn't produced any breakage in the functionality.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (5cbf028) to head (bf755e1).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #149   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           16        16           
  Lines         2264      2274   +10     
=========================================
+ Hits          2264      2274   +10     

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[tacc-tacc]

@5j9

[5j9]

Looks good overall. One thing I'd like to see before merging is a test for each behavior-changing part of the diff, such that reverting that change causes at least one test to fail.

For example, for line 27 of _cell.py, if I revert [^|\r\n] back to [^|\n], all the current tests still pass. I'd like to have at least one test that specifically exercises the \r case and fails when that change is reverted.

In general, I'd like the new tests to make the changes in this PR regression-protected.

[tacc-tacc]

@5j9 Are you still writing the tests? I can write some of them if you want.

[5j9]

Ah, I think I managed to phrase my previous comment badly enough to make it sound like I was going to write the tests myself. Sorry for the confusion!

I meant that I'd like to see the PR updated with tests covering each behavior-changing part of the diff before merging, and I was hoping you would do it. I might eventually add them myself if you don't, but I just don't know when I'll have the free time to do so.

[tacc-tacc]

@5j9 I added some tests and fixes. Can you accept the PR now? PS: you can't use splitlines in _balanced_quotes_shadow because you lose the linebreaks and we need to keep them untouched, so I changed that for regex.sub.