Update typing annotations to track latest practice

[mx-moth]

As we drop support for older versions of Python, newer typing options become available. This task tracks all of these possible improvements, including ones we can not yet implement because we support older versions of Python.

• Replace all typing.List, Set, Dict, Tuple, etc mentions with their plain counterparts (3.9+, PEP 585) (Use Python 3.9 typing features #127)
• Stop using from __future__ import annotations (Use Python 3.9 typing features #127)
• Replace all Union[X, Y] with X | Y (3.10+, PEP 604) (Upgrade to Python 3.10 using pyupgrade #144)
• Use X | None over Optional[X] (3.10+, PEP 604) (Upgrade to Python 3.10 using pyupgrade #144)
• Use generic type parameters def one[T](items: list[T]) -> T:, (3.12+, PEP 695) (Use PEP 695 generics #204)
• Deferred evaluation of annotations, (3.14+, PEP 649 and 749)