Allows pushing to a Vec (or any other type implementing Annexable) with cleanup once result goes out of scope.
e.g.
rust
let mut vec1 = vec![1, 2, 3];
assert_eq!(vec1, [1, 2, 3]);
{
let new_vec_ref = vec1.push_annex(4);
assert_eq!(*new_vec_ref, [1, 2, 3, 4]);
}
assert_eq!(vec1, [1, 2, 3]);
This has the effect of a immutable structure but uses the same underlying allocation (no cloning or additional allocations).