Cache types.GenericAlias in getitems

The "old-style" generic classes from the typing module (List, Dict, etc) cached typing._GenericAlias instances retuned from __getitem__:

>>> from typing import List
>>> List[int] is List[int]
True

But when this functionality was ported to built-in types, caching was not implemented:

>>> list[int] is list[int]
False

Since it is very common to subscript the same types with the same arguments, caching will be very beneficial here and will reduce memory footprint of heavily type-annotated modules.

Linked PRs

• gh-103541

Empieza revisando el comportamiento de caché existente del módulo typing para getitem y el PR vinculado gh-103541. Confirma el resultado deseado con el ejemplo list[int] is list[int]; se considera terminado cuando los alias genéricos integrados equivalentes se almacenan en caché sin cambiar el comportamiento indicado de typing.