Function modwt_multilevel_into 

pub fn modwt_multilevel_into<T: SignalType>(
    data: &[T],
    wavelet: &dyn Wavelet,
    levels: usize,
    per_level_wavelet_out: &mut Vec<Vec<T>>,
    scaling_out: &mut Vec<T>,
) -> Result<()>

Multilevel MODWT writing into caller-supplied output buffers.

per_level_wavelet_out is sized to levels and each inner Vec is resized to data.len(). scaling_out receives the final-level scaling. Rolling- window callers can reuse both across windows; only the two internal ping- pong scratch vecs are freshly allocated per call.