Function quantize_act_q8_1 

pub fn quantize_act_q8_1(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    input_bf16: DevicePtr,
    out_q8: DevicePtr,
    m: u32,
    k: u32,
    stream: u64,
) -> Result<()>

Quantize bf16 activations [m, k] -> q8_1_mmq (DS4 layout) into out_q8.