Implement PEP 692

[JelleZijlstra]

PEP-692 was accepted, but without the syntax change. That means there's very little to do in CPython, but a few changes should be made:

• https://docs.python.org/3.12/library/typing.html#typing.Unpack should mention this new use for Unpack
• https://docs.python.org/3.12/whatsnew/3.12.html should mention the PEP
• Maybe some aspects of typing.py assume Unpack is only used for PEP 646 and should be updated

And maybe something else I'm forgetting.

cc @franekmagiera

Linked PRs

• gh-103629: Update typing.Unpack docs in compliance with PEP 692 #103894
• GH-103629: Update Unpack's repr in compliance with PEP 692 #104048

[franekmagiera]

Thanks Jelle! I will try to find time to pick some of this up after the weekend.

[franekmagiera]

When it comes to typing.py - the repr for Unpack needs to be updated - I will try to do that later this week.

[franekmagiera]

typing rtd already mentions PEP 692, also added a PR to update mypy's cheatsheet

[AlexWaygood]

I think we're done here! Easiest typing PEP to implement that I've been involved with 😄