Function dequant_nvfp4_to_bf16 

pub fn dequant_nvfp4_to_bf16(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    packed: DevicePtr,
    scales: DevicePtr,
    out_bf16: DevicePtr,
    scale2: f32,
    n: u32,
    k: u32,
    stream: u64,
) -> Result<()>

Dequantize NVFP4 weight [n, k] (packed E2M1 + E4M3 group scales + per-tensor scale2) -> bf16 [n, k].