Be more precise than generic `Callable` in type hints

[benoit74]

callback argument of zim.creater.Creator.add_item_for is reported by pyright as partially unknown when in strict mode due to the use of generic Callable.

This is a problem in projects setting pyright in strict mode.

The same generic Callable seems to be an issue in other parts of the code.

We should probably fix this with a more precise type hint,

[rgaudin]

Indeed, we should define a signature/interface for it. It's not like it's used in many ways anyway

[benoit74]

Callable typing issue are fixed with #221, #227 and soon #220 . We might want to define a signature/interface, but this is beyond 5.0.0 for me, so postponing to later.