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<()>

2026-09-25: Quantize BF16 activations [m, k] to q8_1 in out_q8, with k padded to 256. The scale layout (DS4, D4 or D2S6) is the kernel’s.