Devops/drop m2r2 with myst parser

[dennisbader]

Checklist before merging this PR:

• Mentioned all issues that this PR fixes or addresses.
• Summarized the updates of this PR under Summary.
• Added an entry under Unreleased in the Changelog.

Summary

Replaces m2r2 and recommonmark with myst-parser for Sphinx Markdown support, fixing 3 nbconvert vulnerabilities caused by m2r2 pinning mistune==0.8.4.

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.24%. Comparing base (2b1b8a2) to head (1af7a44).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3104      +/-   ##
==========================================
- Coverage   96.31%   96.24%   -0.07%     
==========================================
  Files         161      161              
  Lines       17350    17350              
==========================================
- Hits        16710    16699      -11     
- Misses        640      651      +11     

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