feat(types): updated py::capsule type hint to use new types.CapsuleType

[timohl]

Description

Python 3.13 adds types.CapsuleType.
This PR changes the type hint for py::capsule to the new type.

One open question:
Should I only enable types.CapsuleType for Python Version>=3.13 or for all versions?
Since this only changes type hints/signature it is only in strings and no import is required, so tests still work.
typing.Annotated is already in use without version guard and requires Python Version >= 3.9.
Nanobind falls back to typing_extensions.CapsuleType in previous versions.

Suggested changelog entry:

Updated type hint for ``py::capsule`` to ``type.CapsuleType``

[rwgk]

Looks good to me: capsule never existed as a type (AFAIK), so this seems strictly better.

Waiting to see if @henryiii wants to chime in.

[henryiii]

Fine for now. If we add the fallback someday we should also add it for typing.Annotated.