Function prefill_attention_paged_512 

pub fn prefill_attention_paged_512(
    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,
    stream: u64,
) -> Result<()>

2026-09-25: Causal paged prefill for head_dim == 512 over a BF16 KV cache: 32 query rows and 8 warps per block, with the 101,120 bytes of dynamic shared memory attn_prefill_paged_512.cu requires.