Function compute_phase_laplacian 

pub fn compute_phase_laplacian(
    phase: &[f32],
    mask: &[u8],
    nx: usize,
    ny: usize,
    nz: usize,
    vsx: f32,
    vsy: f32,
    vsz: f32,
) -> Vec<f32>

Compute Laplacian of wrapped phase using the DEL method