Use of generics in requests typing

Currently the requests typing makes heavy use of unions. For example the parameter type is:
https://github.com/python/typeshed/blob/f99e8b0615182bb0f17d9d126019d8d72c207ab3/stubs/requests/requests/sessions.pyi#L97-L103

The issue with this approach is that the type system can't keep track of which type has been chosen for a given field. For example, running pyright on this code:

from requests import Session

session = Session()
session.params = {}
reveal_type(session.params)

Shows us that the type system immediately "forgets" that our parameters are definitely in a dictionary:

test.py:5:13 - information: Type of "session.params" is "dict[str | bytes | int | float, str | bytes | int | float | Iterable[str | bytes | int | float] | None]"
0 errors, 0 warnings, 1 information

If we could make Session (as well as other classes such as Request) generic over the parameter type (as well as other fields), then we could keep track of this kind of state. For example, it might look like:

session: Session[dict] = Session()

Comienza con la sección enlazada de requests/requests/sessions.pyi alrededor de las líneas 97-103 y, después, revisa cómo están tipados Session y Request. Usa el ejemplo de pyright proporcionado para evaluar si los tipos de parámetros genéricos siguen siendo específicos después de una asignación; se considera terminado cuando el diseño genérico propuesto está definido de forma coherente para las clases afectadas y conserva los tipos de campo seleccionados.