Function w8a16_gemv_batch4 

pub fn w8a16_gemv_batch4(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    input: DevicePtr,
    weight: DevicePtr,
    block_scale: DevicePtr,
    output: DevicePtr,
    m: u32,
    n: u32,
    k: u32,
    stream: u64,
) -> Result<()>

Block-scaled FP8 batched GEMV (M<=4). input is [M, K] BF16, output is [M, N] BF16; weight/block_scale are the raw w8a16_gemv pointers (2D block-scaled FP8). One pass over the FP8 weight serves all M rows — the M=4 sibling of w8a16_gemv, replacing w8a16_gemm_pipelined for n<=4 batched decode (which pads M to a 128-row MMA tile). Bit-identical per-row to w8a16_gemv. Grid: (ceil(N/4), 1, 1) Block: (256, 1, 1)