code: async def checkpoint_async(self, event_processor_context=None):
          
          captured_checkpoint = Checkpoint(self.partition_id, self.offset, self.sequence_number)
          await self.persist_checkpoint_async(captured_checkpoint, event_processor_context)
          self.event_processor_context = event_processor_context
docs: Generates a checkpoint for the partition using the curren offset and sequenceNumber for
          and persists to the checkpoint manager.
  
          :param event_processor_context An optional custom state value for the Event Processor.
           This data must be in a JSON serializable format.
          :type event_processor_context: str or dict