Function pad_c_order 

fn pad_c_order<T: Copy + Default>(
    data: &[T],
    dims: [usize; 3],
    out_dims: [usize; 3],
    at: [(usize, usize); 3],
    n_ch: usize,
) -> Vec<T>

Zero-pad a C-order [d0, d1, d2] volume of n_ch-element voxels so the data lands at at.