Function same_alloc::same::for_mut_opt

pub fn for_mut_opt<'a, A: ?Sized>() -> SameLayout<&'a mut A, Option<&'a mut A>>

A proof that any option wrapped mutable reference has same layout as an pure reference. FIXME: this is not const because of the very narrow formulation of https://github.com/rust-lang/rust/issues/57349