Function mbryant_aoc2021::day18::magnitude

pub fn magnitude(number: &Number) -> usize

Compute the magnitude by recursively computing the magnitude for each depth.

For this problem, this is a bit overkill, since the highest magnitude numbers will always be full (2^MAX_DEPTH elements), meaning a recursive approach splitting the number in half each time would work equivalently well. That felt a bit too hacky to me though.