Enhancement: proper fetch* type hinting

[CHerSun]

Current implementation of fetch methods do not type hint objects returned, which makes it more difficult to use.

Suggestion:

Add a TypeVar to fetch.py:

from typing import TypeVar
T = TypeVar('T')

Modify fetch* functions type hinting from:

  def fetch_from(class_: type, obj_id: int) -> Any:

to:

  def fetch_from(class_: type[T], obj_id: int) -> T:

That will give a proper type hint to IDE.