fix: correct type annotations for alive_bar and alive_it

[daniel7an]

Fixes #306

Problem

• alive_bar had no return type annotation, showing up as Any to type checkers
• alive_it returned Iterable[T], hiding the bar handle methods (.text(), .title(), etc.) from type checkers

Changes

• alive_bar now returns AbstractContextManager[__AliveBarHandle], so type checkers know the with statement yields a proper bar handle with text, title, pause, current, monitor, rate, eta, elapsed, and receipt attributes
• alive_it now returns __AliveBarIteratorAdapter[T] instead of Iterable[T], so code like progress.text('...') type-checks correctly while still being recognized as iterable
• Added type annotations on __AliveBarIteratorAdapter for the proxied bar handle attributes
• Added Iterator[T] return type to __iter__
• Made __AliveBarIteratorAdapter properly Generic[T]

Example

# Before: progress.text() would be a type error
progress = alive_it(my_items)
for item in progress:
    progress.text(item.name)  # now type-checks correctly

[rsalmei]

Thanks a lot! That’s fantastic, @daniel7an 👍

[rsalmei]

Oh, sorry, I haven’t merged it yet, @daniel7an. My local repository is quite messed up because I was testing some changes. But I did intend to merge it sometime.