Function execute_single 

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

Default body for every per-op method on Backend — wraps the op in a one-node GraphProto and routes through Backend::execute. Backends that override execute natively (graph-compiling backends) get the per-op surface free; backends that override the per-op methods directly bypass this helper entirely.

attributes carries the ONNX-style per-op attributes the typed per-op signatures encode (ReduceSum’s axes + keepdims, Reshape’s shape, etc.). The walker decodes them back via attr_ints / attr_int / attr_tensor before calling the typed per-op method on the backend.