Switched from mypy to Zuban for static type checking

[agronholm]

NOTE Erasing or replacing the contents of this template will result in your pull
request being summarily closed without consideration!

Changes

Replaced mypy with Zuban as the static type checker. This also moves mypy checks from pre-commit to CI (or tox), as mypy was problematic there for a couple reasons (missing dependencies and inconsistent results).

There are some TODOs left here:

• Zuban cannot determine the type of array.array("i") zubanls/zuban#519 needs to be resolved
• An empty tuple is erroneously deemed incompatible with other iterables zubanls/zuban#520 needs to be resolved
• Default argument values ignored when checking for missing arguments with Unpack zubanls/zuban#521 needs to be resolved
• need to enable testing against the test suite too

Checklist

If this is a user-facing code change, like a bugfix or a new feature, please ensure that
you've fulfilled the following conditions (where applicable):

• You've added tests (in tests/) which would fail without your patch
• You've updated the documentation (in docs/), in case of behavior changes or new
  features
• You've added a new changelog entry (in docs/versionhistory.rst).

If this is a trivial change, like a typo fix or a code reformatting, then you can ignore
these instructions.

Updating the changelog

If there are no entries after the last release, use **UNRELEASED** as the version.
If, say, your patch fixes issue #123, the entry should look like this:

- Fix big bad boo-boo in task groups
  (`#123 <https://github.com/agronholm/anyio/issues/123>`_; PR by @yourgithubaccount)

If there's no issue linked, just link to your pull request instead by updating the
changelog after you've created the PR.