Add Explicit Sync/Async clients, and add mypy types for the library

[intentionally-left-nil]

Fixes #140 This adds mypy type support to the authzed library. The code was almost there already, just needed types for the __init__.py

The challenge with __init__.py is that the Client is either sync or async depending on whether it's in an event loop. Typing this isn't really possible. So, per discord conversation, I broke out two new classes which explicitly are sync or async (and typed those appropriately)

Also, I added a new CI job to validate the types in the future

Test plan: Made sure the py.typed file is present: ❯ tar -tf dist/authzed-0.14.0.tar.gz | grep py.typed authzed-0.14.0/authzed/py.typed ❯ unzip -l dist/authzed-0.14.0-py3-none-any.whl | grep py.typed 0 01-01-1980 00:00 authzed/py.typed

Made sure that mypy passes poetry shell mypy authzed

Made an invalid change to the init.pyi file and validated there was a type error Created a CI job to ensure that the types pass as expected.

recheck

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Couple notes:

1. The types have to be in a __init__.pyi file instead of the code file because the Async definitions (e.g. SchemaServiceAsyncStub) don't exist in the .py files, but only in the .pyi files. (Maybe there's some IF TYPE_CHECKING magic you could use but I thought this way was straightforward)
2. The Client doesn't have any type hints because of the root problem of typing something that is either sync or async
3. It's such a small client that I didn't bother trying to DRY anything up, but let me know if you would prefer for there to be changes