Function `get_disjoint_check_valid`

pub(in ::slice) fn get_disjoint_check_valid<I: GetDisjointMutIndex, const N: usize>(indices: &[I; N], len: usize) -> Result<(), GetDisjointMutError>

This checks every index against each other, and against len.

This will do binomial(N + 1, 2) = N * (N + 1) / 2 = 0, 1, 3, 6, 10, .. comparison operations.