Function iwt_forward_5 

pub fn iwt_forward_5(input: &[i32], output: &mut [i32], scratch: &mut [i32])

Five-level forward IWT decomposition (Section 4.4.4).

Output order: L5, H5, H4, H3, H2, H1 (Eq. 27). buf must have length >= n. scratch must have length >= n.