message: simplified Add creator
diff: @@ -63,12 +63,12 @@ impl<F: PrimeField + SquareRootField> CircuitGate<F> {
  let xor_row = new_row;
  let (and_row, mut gates) = Self::create_xor_gadget(xor_row, bytes * 8);
  let sum = GenericGateSpec::Add {
  - left_coeff: Some(1u32.into()),
  - right_coeff: Some(1u32.into()),
  - output_coeff: Some(-F::one()),
  + left_coeff: None,
  + right_coeff: None,
  + output_coeff: None,
  };
  let and = GenericGateSpec::Add {
  - left_coeff: Some(F::one()),
  + left_coeff: None,
  right_coeff: Some(-F::one()),
  output_coeff: Some(-F::from(2u32)),
  };
  