typing: add initial types

[johnfraney]

Adds initial types and type-checking with Pyright. This contributes to #468 but doesn't finish it.

Notes

There's still a lot of typing to do. I didn't want to introduce any friction to other development, so I didn't add a py.typed file or type-checking in a pre-commit hook or CI. Those are things we can do once we have solid types.

There are times when I'm unsure whether we should be using str or str | bytes/AnyStr, and I tried to get that right through how the variables are used. I hope I got them right.

There are quite a few missing imports in src/textblob/en/__init__.py: https://github.com/johnfraney/TextBlob/blob/dev/src/textblob/en/__init__.py#L1, but that seemed a little out-of-scope for this PR.

Results

Pyright results before:

$ pyright src
[...]
178 errors, 3 warnings, 0 informations

After:

$ pyright
[...]
129 errors, 1 warnings, 0 informations

[sloria]

thanks! looks good on a quick skim 👍

we should add type checking to tox/CI as well, but this can happen in a follow-up PR. I agree this can be an incremental effort. here's how it's set up in marshmallow (with mypy but easy enough to swap it out with pyright

https://github.com/marshmallow-code/marshmallow/blob/944f6de1b7528d87f190e20f132348be360b6e3c/tox.ini#L13-L17

https://github.com/marshmallow-code/marshmallow/blob/944f6de1b7528d87f190e20f132348be360b6e3c/.github/workflows/build-release.yml#L28