Function estimate_normals_gpu 

pub fn estimate_normals_gpu(
    runtime: &WgpuRuntime,
    x: &[f32],
    y: &[f32],
    z: &[f32],
    neighbors: &[u32],
    k: u32,
) -> SpatialResult<Vec<GpuNormal>>

Estimates per-point normals and curvature on the GPU.

neighbors is a flattened point_count * k array of indices into the point arrays, where row i lists the neighbors of point i (pad short rows by repeating the point’s own index). Normal orientation is arbitrary (sign is not disambiguated); callers can flip toward a viewpoint on the CPU.