Contract implementation is unsafe and may trigger UB

[celinval]

Looking at the kani::internal::Pointer implementation for *mut T:

kani/library/kani/src/internal.rs

Lines 59 to 63 in 1491dd6

	impl<'a, T> Pointer<'a> for *mut T {
	type Inner = T;
	unsafe fn decouple_lifetime(&self) -> &'a Self::Inner {
	&**self as &'a T
	}

This can trigger UB if the location pointed by *mut T does not contain a valid value of type T since it is converting it to a &T.
Converting *const T into &mut T and *mut T to &mut T is also unsafe, and may break aliasing rules.

[celinval]

Note that #3363 removes the decouple_lifetime function, but untracked_deref function is still unsafe and my cause UB for arguments that are dropped inside the function.

I was wondering if we can use something similar to Prusti's snapshots: https://viperproject.github.io/prusti-dev/dev-guide/encoding/types-snap.html to replace untracked_deref.