Function pack_contour_vertices 

pub fn pack_contour_vertices(
    device: &Arc<Device>,
    queue: &Arc<Queue>,
    inputs: &ContourGpuInputs<'_>,
    params: &ContourGpuParams,
) -> Result<GpuVertexBuffer, String>

Builds a GPU-resident vertex buffer for contour plots directly from provider-owned Z data.