Function optimize_cover 

pub fn optimize_cover(
    pixels_rgb: &[u8],
    width: u32,
    height: u32,
    config: &OptimizerConfig,
) -> Vec<u8> 

Optimize raw RGB pixels for steganographic embedding.

Returns a new pixel buffer with the same dimensions and format (RGB, 3 bytes per pixel, row-major). The modifications are subtle enough to be imperceptible (PSNR > 44 dB, SSIM > 0.993) but improve embedding capacity by increasing wavelet energy in smooth regions.

If the optimization would reduce gradient energy (degrade stego capacity), the original pixels are returned unchanged.