add turtledemo module

[tungol]

This isn't terribly useful, but they're not that complicated either.

[JelleZijlstra]

I'd like to hear what other maintainers think, but I'm not sure this is worth adding. It's a reasonably large amount of code to maintain, and it's clearly not meant for people to import.

[tungol]

That's fair. I think the code is relatively stable, although I did discover that turtledemo.clock had a bugfix for 3.12+.

Like you say, it's not meant for importing, but the source code is meant for reading by end users of python. When you run the demos, the source code is displayed alongside the animation. So I think that the value of the stubs is the same: a user can read them alongside the source of the demos, if they're so inclined. On the hand, the primary type of user who would benefit from examining the source code of the demos is less likely to know about typeshed.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉