Update typehints to use intrinsic types

[arporter]

With #2837 we are dropping support for python 3.7 and 3.8 (they are well past EOL) and skipping on to 3.10.

As such, we can now use intrinsic types in type hints, e.g.:

guard_type: list[str | None] = field(default_factory=list)

instead of:

from typing import List, Union
...
guard_type: List[Optional[str]] = field(default_factory=list)

This will be addressed in a "you touch it, you fix it" manner so it's up to code reviewers (@LonelyCat124 @sergisiso @hiker @TeranIvy) to enforce this :-)