Chore: add ability to test code snippets from the docs

[talagluck]

Description

[tychoish]

this is pretty difficult to get right (because you need setup code in many cases that you don't want to display, and synchronization with upstream repos and versioning can be kind of hard.

I would:

• see if mdbook (which I desire to use) has support for this kind of doctest/literate programming functionality.
• if we have to implement it ourselves, the "best" solution is to put all of the "tested" documentation code samples in individual files, potentially in a separate repository, and then inline them in their entirity into the documentation.

[talagluck]

I previously used Docusaurus, and this was possible. There were a bunch of gotchas to it, and we wound up writing some additional checkers to make sure the right code snippets were the ones that were embedded, but it was a really nice feature to have. I'll poke around and see if this might be possible with mdbook.