SIMD is true, but the original guess is correct, and that effect is bigger!

using_map is faster because it's not allocating: it's re-using the input array. That is, it is operating on the input `v` value in place, equivalent to this:

    pub fn using_map(mut v: Vec<i32>) -> Vec<i32> {
        v.iter_mut().for_each(|c| *c += 1);
        v
    }

This is a particularly fancy optimization that Rust can perform.