Function sigmoid_gate_mul 

pub fn sigmoid_gate_mul(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    input: DevicePtr,
    gate: DevicePtr,
    output: DevicePtr,
    num_elements: u32,
    stream: u64,
) -> Result<()>

Element-wise sigmoid gate: output[i] = input[i] * sigmoid(gate[i]).

Used for gated attention in Qwen3: attn_output = attn_output * sigmoid(q_gate).

Kernel: sigmoid_gate_mul(input, gate, output, n) Grid: (ceil(n/256), 1, 1) Block: (256, 1, 1)