code: def highest_stored_id(self):
          
  
          shared = [0]
          def _keep_max(_i, reading):
              if reading.reading_id > shared[0]:
                  shared[0] = reading.reading_id
  
          self.engine.scan_storage('storage', _keep_max)
          self.engine.scan_storage('streaming', _keep_max)
  
          return shared[0]
docs: Scan through the stored readings and report the highest stored id.
  
          Returns:
              int: The highest stored id.