Fix typing of Timezone and ZoneInfo

[bryanforbes]

Currently the method used to import zoneinfo leaves it typed as Any in mypy and Unknown in pyright. This PR updates pendulum.utils._compat to inform type checkers of the correct type information for zoneinfo while leaving the import mechanism the same during runtime. With Timezone having the correct type info from ZoneInfo, a few more type errors surfaced which I took care of either by adding/removing # type: ignore or adding/removing cast() calls. Since no logic has changed at runtime, no unit tests were added.

[Secrus]

will having only the TYPE_CHECKING part satisfy mypy? we are using pyupgrade, which understands this type of syntax (unlike try-ImportError) and handles it when upgrading.

[bryanforbes]

will having only the TYPE_CHECKING part satisfy mypy? we are using pyupgrade, which understands this type of syntax (unlike try-ImportError) and handles it when upgrading.

If you are asking if the whole if TYPE_CHECKING/else block can be simplified to just the version check condition, the answer is yes. That whole block can be simplified to:

if sys.version_info < (3, 9):
    from backports import zoneinfo
else:
    import zoneinfo

This will work at runtime and during type checking (in both mypy and pyright and I would suspect other type checkers as well). IMO the simplified version is the better solution, but I was trying to make as few changes to the runtime behavior as possible.

[Secrus]

Go with this solution, please. We are going into 3.0 anyway, so it's ok if there are some changes.

[bryanforbes]

I've updated PR to address this