Add annotations for type-specific rustworkx functions

[IvanIsCoding]

Closes #960
Related to #352, follow up of #401

This adds type annotations to all type-specific rustworkx functions. It also re-exports all type-specific functions at the top-level, because it is unlikely that users will use rustworkx.rustworkx (it's a hidden implementation detail)

[coveralls]

Pull Request Test Coverage Report for Build 6962670551

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 95.882%

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Totals
Change from base Build 6952364260:	0.0%
Covered Lines:	15577
Relevant Lines:	16246

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💛 - Coveralls

[IvanIsCoding]

This is ready for review, I hope it makes it to 0.14

[mtreinish]

Overall this looks great, thanks for spending all the time to fix this. Just a couple of questions inline.

[mtreinish]

Do we have to worry that this adding a module that doesn't exist in the rustworkx package? Like we'll have type hints for rustworkx.cartesian_product.digraph_cartesian_product which isn't a valid path in rustworkx.

[IvanIsCoding]

The linter complains but it’s a tradeoff. I created the files to organize our code like in Rust. But in practice our Rust just becomes one big file, while Python doesn’t. I could try adding underscores in the name of the files to prevent them from being imported following PEP-8 conventions