code: async def find(self, seq_set: SequenceSet, selected: SelectedMailbox,
                     requirement: FetchRequirement = FetchRequirement.METADATA) \
              -> AsyncIterable[Tuple[int, MessageT]]:
          
          for seq, cached_msg in selected.messages.get_all(seq_set):
              msg = await self.get(cached_msg.uid, cached_msg, requirement)
              if msg is not None:
                  yield (seq, msg)
docs: Find the active message UID and message pairs in the mailbox that
          are contained in the given sequences set. Message sequence numbers
          are resolved by the selected mailbox session.
  
          Args:
              seq_set: The sequence set of the desired messages.
              selected: The selected mailbox session.
              requirement: The data required from each message.