[tzdata] Add package stubs

[StanFromIreland]

tzdata is a first-party package and generally data-only, except for these two constants (and we don't plan on adding any more).

[github-actions]

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

[donBarbos]

Thank you! But given that tzdata is well supported, and adding its own stubs or type annotations to the library itself is the preferred method of distributing type information, I suggest the package itself distribute these types (along with the py.typed).
What do you think about?

[StanFromIreland]

I’m split on this, if we were to add them we would be further straying from the idea of „data-only”.

[donBarbos]

It might be worth opening issue to gather Paul Ganssle’s input on this. Until then, it seems reasonable to keep the current types in typeshed, considering Paul might not be available in the near term.

[srittau]

Thanks!

[StanFromIreland]

FYI I messaged Paul.

[StanFromIreland]

FTR Paul also doesn’t support moving them to the package itself, they will be staying here.