Function w4a16_gemv_qg_batch2 

pub fn w4a16_gemv_qg_batch2(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    input: DevicePtr,
    weight: &QuantizedWeight,
    output: DevicePtr,
    n: u32,
    k: u32,
    num_heads: u32,
    head_dim: u32,
    stream: u64,
) -> Result<()>

2026-09-25: w4a16_gemv_qg for 2 rows: A is [2, K], C is [2, N], each row deinterleaved.