Function gen_qwen38_prefill_layer_lg 

pub fn gen_qwen38_prefill_layer_lg(
    cfg: &Qwen38Cfg,
    l: usize,
    dir: &str,
    ctx: usize,
    pos0: usize,
    chunk: usize,
) -> Authored

Layer l of a prefill chunk of chunk rows from pos0 alone.