Handling `mkdocs` vs `properdocs`

[domWalters]

mkdocs has slowly collapsed from a maintenance perspective over the last 2 years:

https://fpgmaas.com/blog/collapse-of-mkdocs/

This means that:

• mkdocs v1.x will likely receive no further support
• mkdocs v2.x will break everything

Additionally, mkdocs-material is also in maintenance mode due to the above.

There are alternatives that have sprung up:

• properdocs to replace mkdocs from the last active maintainter of mkdocs
  • https://github.com/ProperDocs/properdocs
• mkdocs-materialx to replace mkdocs-material
  • https://github.com/jaywhj/mkdocs-materialx

Ultimately, these issues don't have to be handled yet, only when something breaks. However, IMO:

• We should be interoperable with these alternatives.
• We should prefer these alternatives.
• We should version limit mkdocs to 1.6.1 and not accept anything newer, given the current state of the maintainership.