message: set_grad_enabled propagate jit label to AD variable
diff: @@ -1574,6 +1574,11 @@ struct DiffArray : ArrayBase<value_t<Type_>, is_mask_v<Type_>, DiffArray<Type_>>
  if (m_index > 0)
  return;
  m_index = detail::ad_new<Type>(nullptr, width(m_value));
  + if constexpr (is_jit_array_v<Type>) {
  + const char *label = m_value.label_();
  + if (label)
  + detail::ad_set_label<Type>(m_index, label);
  + }
  } else {
  if (m_index == 0)
  return;
  