Function vae_conv2d 

pub fn vae_conv2d(
    w: &[f32],
    bias: &[f32],
    x: &[f32],
    ic: usize,
    oc: usize,
    h: usize,
    w_img: usize,
    k: usize,
    out: &mut [f32],
) -> bool

VAE conv2d on the device (implicit GEMM — the CPU path pays for a multi-GB im2col matrix at high resolutions).