MAINT: Encapsulate config import

[larsoner]

This PR moves toward simplification of config.py by:

1. Doing a lot of copy-paste to _whatever.py files from config.py (looks like ~1700 lines removed from config.py)
2. Removing all import config / from config import from the top of scripts in favor of relative imports of from ..._whatever import ...
3. Fixing a number of bugs with broken encapsulation demonstrated by (2)
4. Removes the workarounds present in docs that are no longer needed

We'll see how much stuff fails. Once it's green I think we can merge. Then hopefully just one more PR will be necessary to move the "input validation" stuff out of config.py that is left at the end of the file.

[larsoner]

Ready for review/merge from my end

[hoechenberger]

@larsoner This will need a merge / rebase on main once #634 has been merged

Also I'd kindly ask to hold off merging this until I've finished working on #625 – it's my fourth (or so) attempt to get CSP into the pipeline, and I've had to spend so much time rebasing / restarting because upstream changes kept on piling up … I don't want to have to do this again! So please give me a chance to get #625 finished before we proceed here :)

[agramfort]

looks good !

@hoechenberger what's the status on CSP? Can I help?

[hoechenberger]

@larsoner Why did you remove the Optional type in many places?

Maybe there's a (common) misunderstanding here: Optional[foo] is actually shorthand for Union[None, foo], which can (finally!!) be written as None | foo in Python 3.10 (this was sooo overdue).

You can, therefore, have a required parameter that is nevertheless annotated with an Optional type if it's allowed to be None.

[larsoner]

Ahh yes whatever can be None can be restored then. Or maybe we should just wait until 3.10 is the minimum requirement and use the nicer syntax. Up to you

[hoechenberger]

@larsoner I think this is good to merge from my end now, thank you. but please hold off for now if possible so I can get #625 finalized first

[larsoner]

Works for me

[larsoner]

Now that #625 is working and I've seen what's required, I'll merge this and fix any conflicts. I don't think they'll be too bad!