Additional Vector::ptr_eq confusions

[cmyr]

Trying to understand what behaviour I should expect from Vector::ptr_eq.

In particular, I am surprised that the following test passes:

#[test]
fn ptr_eq_huh() {
    let smol = std::iter::repeat(42).take(64).collect::<Vector<_>>();
    let mut smol2 = smol.clone();
    assert!(smol.ptr_eq(&smol2));
    smol2.set(63, 420);
    assert!(!smol.ptr_eq(&smol2));

    let huge = std::iter::repeat(42).take(65).collect::<Vector<_>>();
    let mut huge2 = huge.clone();
    assert!(huge.ptr_eq(&huge2));
    huge2.set(63, 420);
    assert!(huge.ptr_eq(&huge2));
}

That is: with 64 elements the ptr_eq returns false after mutation, and with 65 elements (and any more than that, as far as I've tested) it returns true.

I assume this is just a bug, but nothing has jumped out at me. I'll look at this a bit more, but curious for any guidance.

[cmyr]

Ok, I have a maybe-solution up at #132? 🤷