title: open62541: get all changed monitored items of subscription at the same time
body: <p>As far as I can see from the OPC-UA specifications, on every publishing interval OPC-UA server sends one NotificationMessage containing all Notifications of all changes (I'm monitoring variable values) it has sampled in queue.</p>
  
  <p>But as I found in open62541 documentation, its subscription methods <code>UA_Client_MonitoredItems_createDataChange</code> and <code>UA_Client_MonitoredItems_createDataChanges</code> work on "callback per every single monitored item" basis. Item by item.</p>
  
  <p>Is there a way to get all the monitored items changes of one publishing interval in bulk?</p>
  
  <p>1-st publishing interval: changed values of items 1, 2, 3</p>
  
  <p>2-nd publishing interval: changed values of items 2, 4, 5</p>
  
  <p>etc...</p>