Improve internal and downstream type checking

[daneah]

This change is a: (check at least one)

• Bugfix
• Feature addition
• Code style update
• Refactor
• Release activity

Is this a breaking change? (check one)

• Yes (for type checking)
• No

Is the:

• Title of this pull request clear, concise, and indicative of the issue number it addresses, if any?
• Test suite passing?
• Code coverage maximal?
• Changelog up to date?

What does this change address?

We added py.typed files in #111 but they would only appear in the source distribution through MANIFEST.in; include_package_data = True is required for the files to land in the binary wheel distribution.

We've also got a few things to get up to speed on regarding tooling configuration.

How does this change work?

• Set include_package_data = True in setup.cfg.
• Update Optional syntax to comply with PEP 484 and mypy's more strict checking of it
• Update GitHub Actions config to use stable version of Python 3.10
• Add Python 3.11 configurations for tools where necessary
• Stop ignoring imports during type checking

Additional context

This can break consumers' type checking because this package would have previously needed to be ignored by mypy for lack of types; now it can be included, but consumers may find their usage does not type check.