Eliminate: from __future__ import annotations, after upgrade to Python 3.13+

[davidfstr]

The way of declaring annotations enabled by this future is considered deprecated, in favor of PEP 649 deferred annotations, although those annotations will only be fully available when Crystal only supports Python 3.13+

In the meantime:

• Eliminate the __future__ import
• Stringify annotations as needed in response

[davidfstr]

I started work on this on branch f/remove_future_annotations.

It looks like far too many annotations would need to be stringified as a response to removing from __future__ import annotations, so it may be worth cancelling this feature altogether, in favor of waiting for upgrade to Python 3.13 where PEP 649 will be available.