Function gdn_prefill_persistent_smem 

pub fn gdn_prefill_persistent_smem(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    h_state: DevicePtr,
    query: DevicePtr,
    key: DevicePtr,
    value: DevicePtr,
    gate: DevicePtr,
    beta: DevicePtr,
    output: DevicePtr,
    batch_size: u32,
    seq_len: u32,
    num_k_heads: u32,
    num_v_heads: u32,
    k_dim: u32,
    v_dim: u32,
    qk_stride: u32,
    v_stride: u32,
    gb_stride: u32,
    smem: u32,
    stream: u64,
) -> Result<()>

Persistent GDN prefill with explicit shared memory size. Used for WY4-persistent variant which needs more shared memory.