typing: explicitly type some `mercurial.util` eol code to avoid @overload Unlike the previous commit, this makes a material difference in the generated stub file- the `pycompat.identity()` aliases generated an @overload like this: @overload def fromnativeeol(a: _T0) -> _T0: ... ... which might fail to detect a bad argument, like str. This drops the @overload for the 3 related methods, so there's a single definition for each. The `typelib.BinaryIO_Proxy` is used for subclassing (the same as was done in 8147abc05794), so that it is a `BinaryIO` type during type checking, but still inherits `object` at runtime. That way, we don't need to implement unused abstract methods.