Function pack_chw 

pub fn pack_chw<T, const CHANNELS: usize>(
    input: ImageView<'_, T, CHANNELS>,
    scale: f32,
    mean: [f32; CHANNELS],
    std: [f32; CHANNELS],
) -> Result<PlanarImage<f32, CHANNELS>, VisionError>
where
    T: PixelComponent,

Packs and normalizes an interleaved image into planar CHW storage.