feat: Use mdformat to format Markdown pages

[pawamoy]

It handles most of custom markup thanks to mdformat-mkdocs.

[pawamoy]

uv tool install mdformat --with mdformat-mkdocs

mdformat docs --number --wrap no --extensions mkdocs --extensions tables --ignore-missing-references

Things to fix:

• Separation lines --- (<hr>) are transformed to ____________, it's especially problematic for front-matter metadata. Fixed with https://pypi.org/project/mdformat-simple-breaks and https://pypi.org/project/mdformat-frontmatter.
• Footnote blocks are escaped and inlined. Problematic. Fixed with https://pypi.org/project/mdformat-footnote.
• Non breaking spaces   are replaced with regular spaces. WTH? 😂
• Spaces are inserted between > and ? for markdown-callouts. Fixable by switching to GitHub's callouts, though they do not support titles.
• Tables padding is either expanded, or removed. No option to retain existing padding, or to expand/compact given a user-specified width. Also first and last columns of | are added, while unnecessary.
• Blank lines are added after # YORE comments. Problematic since it's important not to have a blank line there.
• Underscores are escaped in mkdocstrings ::: identifiers. Problematic.
• Underscores are escaped in attr list { target="\_blank" }. Not critical if that doesn't break the targets.
• The frontmatter extension formats the YAML. I don't like extraneous indentation in YAML. Not critical though.
• Code blocks containing an indented ``` string are changed to use 4 backticks, while it's not needed. Not critical.
• mkdocstrings ::: blocks are inlined. Fixable by adding a blank line before options, unless they're wrapped in fences.
• pymdownx blocks are inlined. Fixable by adding blank lines around contents.
• Markdown anchors are inlined with following paragraph. Makes sense. Fixable by adding a blank line.
• References ids are removed when equal to lowercase title: [Insiders][insiders] -> [Insiders]. Annoying. I'd like to at least retain [Insiders][] for better syntax highlighting in editors.