Function nvfp4_mmq_quantize_act 

pub fn nvfp4_mmq_quantize_act(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    input_bf16: DevicePtr,
    out_y: DevicePtr,
    m: u32,
    k: u32,
    stream: u64,
) -> Result<()>

2026-09-25: Quantize BF16 activations [m, k] to block_fp4_mmq in out_y: E2M1 values with one UE4M3 scale per 16, k padded to 256, one thread per 16-value group.