Improve library typing

[CrisMystik]

This pull request aims to improve Pyrogram/Kurigram's type hinting through the following changes:

• Type-hint all "public" fields and methods (previously, some of them were missing a type annotation)
• Fix some typing errors, for example: many fields were like parameter: Union[X, Y] = None, which is incorrect (it should be Union[X, Y, None])
• Add type-hints for handlers and decorators, and filters
• Add a basic type-hint for progress callbacks

Other changes that I still have not made:

• Make all raw.types.* classes inherit from their respective raw.base.* classes - and mark the latter as abstract classes already being worked on by feat(cod-gen): change raw types generation to have proper typehints #130 apparently
• Find a better way to annotate functions that return a different type based on their parameters (e.g. download, get_users)
• Add type hinting for invoke() using generics

[KurimuzonAkuma]

parameter: Union[X, Y] = None, which is incorrect (it should be Union[X, Y, None])

i prefer Optional[Union[X, Y]]

[m2k7m]

there are two Optional

[m2k7m]

i think it should be Optional[Union[int, str, raw.types.RpcError]]

[Danipulok]

Make all raw.types.* classes inherit from their respective raw.base.* classes - and mark the latter as abstract classes already being worked on by #130 apparently

#130 was closed in favor of #151 that was merged today.
Also, you shouldn't change a few things in the same PR.

Find a better way to annotate functions that return a different type based on their parameters (e.g. download, get_users)

Again, should be a separate PR. You can also add get_user (I've thought about this for a while), and use @typing.overload for download function. And maybe add @typing.overload to get_users too, since it's used a lot.

Add type hinting for invoke() using generics

I don't quite think there's a way to do this via generics. But maybe there's a hack. Most probably it'd be a separate generator function that creates file with @typing.overload for all possible invoke outcomes.

[Danipulok]

@CrisMystik why is it draft, though?
What's here to be done?

[Danipulok]

@CrisMystik are you still willing to finish this?

[KurimuzonAkuma]

@CrisMystik are you still willing to finish this?

я живой?

[Danipulok]

@CrisMystik are you still willing to finish this?

я живой?

надеюсь.