Update to eslint@9

[GregRos]

Some more changes to linting:

• Adds a markdownlint-cli2 file with settings that worked well for me in some other projects
• Exclude prettier from touching markdown. Tends to be too aggressive.
• Enable linting code blocks in markdown using ESlint markdown processor.
• Code blocks are linted using ESLint's stylistic plugin configured not to wrap any code. Code blocks should be manually wrapped for maximum readability.

Regarding eslint@9:

• Migrates to flat config file format.
• Updates linting packages and plugins.
• Keep the same rules, with one or two exceptions.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.91%. Comparing base (528a377) to head (060ffb4).
⚠️ Report is 7 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #138   +/-   ##
=======================================
  Coverage   94.91%   94.91%           
=======================================
  Files          63       63           
  Lines        1808     1808           
  Branches      209      209           
=======================================
  Hits         1716     1716           
  Misses         92       92           

Flag	Coverage Δ
char-info	99.77% <ø> (ø)
parjs	93.35% <100.00%> (ø)

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