Use Sybil for doctests

[nstarman]

This PR add docstring testing and testing of the docs via Sybil (https://sybil.readthedocs.io/en/latest/).
I'm not sure what style of docstrings you want... My last PR was in the NumPy style, but the rest of the docs are in Google's...

If you don't like the try: ...; ... except Exception as e: print(f"{type(e).__name__}: {e}"), I think we can subclass sybil.parsers.myst.PythonCodeBlockParser and modify it so that the try: except operates behind the scenes. IMO I like that it's explicit and the examples are safer to copy-paste.

Found:

• 1 bug (plum/util.py) where classes generated in an atypical fashion, e.g. as in the docs have __module__ is None
• Many out-of-date / incorrect docs — including the ones I just contributed!

Squash merge is fine!

[nstarman]

Hmm. This passes on py3.12 on my local version.

[coveralls]

Pull Request Test Coverage Report for Build 8786086897

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 8773615289:	0.0%
Covered Lines:	1219
Relevant Lines:	1219

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💛 - Coveralls

[nstarman]

I think the failure is unrelated

[wesselb]

This looks awesome, @nstarman. Thank you so much for this!

I've got a few very minor comments/questions, which I left as comment in the PR.

[wesselb]

Again, this is a fantastic PR, @nstarman! Merging this right away. :) Thanks so much!!