Function conv_3x3_simd 

pub fn conv_3x3_simd(
    input: &[f32],
    kernel: &[f32],
    output: &mut [f32],
    in_h: usize,
    in_w: usize,
    in_c: usize,
    out_c: usize,
    stride: usize,
    padding: usize,
)

SIMD-accelerated 3x3 convolution with automatic architecture dispatch