[types] incomptabile assignment types due to invariant and type union

[rchui]

Instead of using type unions (like used here https://github.com/typesense/typesense-python/blob/master/src/typesense/types/collection.py#L226-L232), the library should use bound typevar like:

a: list[int | str]
b: list[int] = [1]

a = b  # failure: incompatible assignment due to invariant

from typing import TypeVar

ListT = TypeVar("ListT", bound=int | str)

c: list[ListT]
d: list[int] = [1]
e: list[str] = ["a"]
f: list[int | str] = [1, "a"]

c = d  # success
c = e  # success
c = f  # success

The type checkers are really unhappy with the way that the types are currently formulated. I should be able to supply a list of just RegularCollectionFieldSchema to CollectionUpdateSchema. Instead it errors due to the type construction. I shouldn't have to reverse engineer the internal union type to satisfy the type checker.