Function build_pad_rows 

pub fn build_pad_rows<F: TowerField + HardwareField>(
    layout: &OuterLayout,
    pad: &[Flat<F>],
    code_len: usize,
    filler: &[Flat<F>],
) -> Result<Vec<Vec<Flat<F>>>>

PAD oracle rows: the pad in OuterLayout::slot order, filler (exactly pad_rows · (code_len - message_len) entries) on the message tail.