Feature: `covers` annotation/attribute should tell psalm that method is in use

[boesing]

When using @covers, I would expect psalm to realize that a method is in use, even tho, it is not directly called.

AFAIR, @psalm-api does mark methods as used as well, even tho they might not be called - so there is not a strong need in actually verifying that, right? Thoughts?

[orklah]

Seems good to me