types: make everything type check

[Gobot1234]

Summary

Use more 3.7+ features in the library and make everything type check. This also adds support for using the union operator for python 3.10+ for Union/Optional

Checklist

• [x] If code changes were made then they have been tested.
  • [x] I have updated the documentation to reflect the changes.
• [ ] This PR fixes an issue.
• [ ] This PR adds something new (e.g. new method or parameters).
  • [ ] This change has an associated test.
• [ ] This PR is a breaking change (e.g. methods or parameters removed/renamed)
• [ ] This PR is not a code change (e.g. documentation, README, ...)

[Gobot1234]

No idea where this pkg_resources failure came from

[Gobot1234]

@cetanu do you have any idea why the tests are failing?

[cetanu]

Looking now...

[cetanu]

It appears to be related to this

https://github.com/grpc/grpc/issues/33570

but it's just a deprecation warning? I think we can catch this

[cetanu]

https://github.com/grpc/grpc/blob/master/tools/distrib/python/grpcio_tools/grpc_tools/protoc.py#L21

[cetanu]

Since this is only for generating the tests, we could do something very hacky

    import re
    from importlib import resources

    file = resources.files("grpc_tools") / Path("protoc.py")
    content = file.read_text()

    if "import pkg_resources" in content:
        content = re.sub(
            pattern="import pkg_resources",
            repl=r"try:\n    import pkg_resources\nexcept DeprecationWarning:\n    pass",
            string=content,
        )

    file.open().write(content)

[Gobot1234]

I'll just send a PR to fix it

[tzahush]

@Gobot1234 I see the PR that we were waiting for here https://github.com/grpc/grpc/pull/35329 is closed, what should we do as next steps? perhaps this was fixed in different PR's.