Function mla_prefill_attention_320 

pub fn mla_prefill_attention_320(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    q: DevicePtr,
    k: DevicePtr,
    v: DevicePtr,
    output: DevicePtr,
    seq_len: u32,
    batch: u32,
    num_q_heads: u32,
    num_kv_heads: u32,
    head_dim: u32,
    inv_sqrt_d: f32,
    causal: bool,
    stream: u64,
) -> Result<()>

MLA absorbed prefill attention (HDIM=320, simple scalar kernel). Grid: (num_q_heads, ceil(seq_len/16), batch) Block: (256, 1, 1)