Function prefill_attention_paged_bf16k_turbo4v_64 

pub fn prefill_attention_paged_bf16k_turbo4v_64(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    q: DevicePtr,
    k_cache: DevicePtr,
    v_cache: DevicePtr,
    output: DevicePtr,
    block_table: DevicePtr,
    q_len: u32,
    kv_len: u32,
    q_offset: u32,
    num_q_heads: u32,
    num_kv_heads: u32,
    head_dim: u32,
    cache_block_size: u32,
    sliding_window: u32,
    inv_sqrt_d: f32,
    v_block_stride_bytes: u64,
    v_data_section_bytes: u64,
    stream: u64,
) -> Result<()>

Prefill paged attention — TurboQuant+ safer-asym Bf16K + Turbo4V (BR=64).

Same kernel ABI as prefill_attention_paged_bf16k_turbo3v_64; the underlying kernel uses a 4-bit V dequant path in LOAD_V_TILE.