Function build_edges 

fn build_edges(
    phase: &[f64],
    mask: &[u8],
    reliability: &[f64],
    nx: usize,
    ny: usize,
    nz: usize,
) -> Vec<Edge>

Build the 6-connected edge list, skipping any pair with a masked endpoint.

Emitted in x, then y, then z order, matching the reference’s horizontalEDGEs/verticalEDGEs/normalEDGEs — the order decides how equal reliabilities are broken in sort_edges.