[FEATURE] Do not remove explicitly re-exported imports even if unused

[gandhis1]

Mypy will prevent users from doing implicit re-exports. So if in module a you do from b import obj, and attempt to do from a import obj elsewhere, that will error. See https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-no-implicit-reexport for more context.

There are two ways in which you can explicitly re-export. They are:

1. When you import and set the __all__ attribute in an __init__.py. pycln as far as I remember has no problem with this.
2. When you use the explicit re-export syntax that is supported by Mypy, which is from b import obj as obj. This signals to Mypy that you are intentionally, deliberately re-exporting this, and are permitting imports of obj through module a.

It appears that 2 is not respected by pycln. It will remove these re-exports, because they are unused. So the feature request here is that pycln respects this convention and does not remove these. I understand that these are easily silenced through the comment directives, but the ask here is to make that superfluous.

[Avasam]

Yes please. Explicit re-exports using as as a standard is kinda new, and has been quite popularized in stubs. But it's a useful signal in .py files too ! You're already telling tools "this is meant to be used outside this module", pycln should understand it too.

This should also be a valid way to resolve undecidable cases where "Pycln can not decide whether the unused imported names are useless or imported to be used somewhere else (exported)."