Function plotpx_write_heatmap_png_file 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn plotpx_write_heatmap_png_file(
    path_ptr: *const c_char,
    points_ptr: *const PlotpxHeatmapPoint,
    points_len: usize,
    width: u32,
    height: u32,
    saturation: f32,
    color_ptr: *const u8,
    color_len: usize,
) -> c_int