Type annotations for base spec

[slmnsh]

Fixes #625

[martindurant]

Some thoughts.

My biggest gripe is the extended overrides, mostly because of detail=True|False.

[slmnsh]

@martindurant Thanks for review! I think I should've started with type stubs then later maybe add inline types. type stubs will be cleaner to add than inline types.

I will push type stubs this weekend.

[slmnsh]

@martindurant I have added completely separate type stub file. I am planning to add more for known implementations once you review this

[martindurant]

Much happier with the annotations separate :). Now the main code is not affected, nor even import times. Do you have any thoughts on how best to keep the code and types in sync in the future?

[slmnsh]

mypy has stubtest for testing stub maybe we can incorporate that

https://mypy.readthedocs.io/en/stable/stubtest.html#automatic-stub-testing-stubtest

[martindurant]

Can you please draft a non-required CI run with that, and text instructions for how to go about updating types in the future as the API changes?

[slmnsh]

@martindurant Sorry for delays. I added "Run Stub Tests" step for running stub test it will raise error if failed and instructions to readme.