Use TypeAlias

[tekktrik]

The library docs substitute things like ReadableBuffer with the full Union, and I'm wondering if typing it explicitly as a TypeAlias might help. Either way, it's more documentation.

• Adds TypeAlias type annotation to type aliases
• Because behind the scene importing something from typing_extnesions that is available from typing will just import it from there, I've removed the try/except block for testing, but only for simplicity.
• TypeAlias is available in any 4.0 compatible release of typing_extensions
• Similarly, I've removed the Python<3.7 conditional since now everything under 3.10 will need it, which is the other reason to just safely import things from typing_extensions.
• pylint got real mad all of a sudden about unused-argument and no-self-use warnings resulting from Protocol definitions, so they've been disabled permanently. I didn't see any issue with this since this library is non-functional in purpose, but happy to change it if there's a better solution.

[FoamyGuy]

Looks good to me.

simplifying our imports by leveraging the internal checking is welcome I think.

Also seems fine for this library to disable those specific pylint checks since everything in here is intended for defining types rather than being function and doing things.

Thank you @tekktrik