Function execute_multi 

pub fn execute_multi<B>(
    backend: &B,
    op_type: &str,
    inputs: &[&<B as Backend>::Tensor],
    attributes: Vec<AttributeProto>,
    output_count: usize,
) -> Result<Vec<<B as Backend>::Tensor>, <B as Backend>::Error>
where
    B: Backend + ?Sized,

Default body for multi-output per-op methods (Backend::split today). Builds a one-node GraphProto with output_count positionally-named outputs, calls Backend::execute, and extracts the outputs in declared order.

If output_count == 0, returns an empty Vec without invoking execute — multi-output ops with zero outputs are degenerate and the engine never produces such carriers.