[Feat] Add type hints

[fjosw]

As a first step towards adding type hints, I added automatic type hints with monkeytype. Hints for the more complicated methods will need additional manual work but for the simpler methods this seems to have worked quite well.

[fjosw]

Not quite done but already in decent shape for a review @s-kuberski @jkuhl-uni:

• Most of the changes are just type annotations
• I changed a few lines to help mypy with understanding the type annotations
• I fixed a few smaller bugs in which explicit type checks were not consistent or did not cover certain edge cases

For now I ignored the input/* modules and most of correlators.py, the remaining modules only raise a few smaller mypy errors which I wasn't able to fix right away.

[s-kuberski]

Great, thanks a lot for all of your work! I'll have a look in the upcoming week.

[jkuhl-uni]

Shouldn't this be list[Obs]? Alternatively, in the list, there could be something Obs-like, I suppose, such as list[CObs]?

[jkuhl-uni]

Hey @fjosw,
thanks for all the work, I am looking through it right now, it looks excellent to me. I hope it was okay that I pushed a few small changes. If not, feel free to revert them, as you please :)

[fjosw]

I resolved the merge conflicts and fixed a few smaller issues but now one of the tests test_rwms is failing. Can you have a look @jkuhl-uni ?

[jkuhl-uni]

I had a look and found a solution for now, there are a few minor things to figure out. I hope to get it done today :)

[jkuhl-uni]

... well that was easy.
I'd like to disentangle some of the openQCD tests (in test_rwms we are testing the read_rwms, extract_t0 and extract_w0 methods), but I'll do that in a different PR.

[fjosw]

Thanks a lot @jkuhl-uni ! As we have accumulated quite a few changes I would suggest that we all do a thorough review and then merge this first version with type hints which we can refine later @s-kuberski @jkuhl-uni .