message: Refactor batch matching
  Quick minor cleanup of internal batch stream message matching.
diff: @@ -168,27 +168,22 @@ impl Stream for BatchIter {
  if self.pending_messages == 0 {
  return std::task::Poll::Ready(None);
  }
  +
  match self.subscriber.receiver.poll_recv(cx) {
  - std::task::Poll::Ready(message) => {
  - if let Some(mut message) = message {
  - message.status = match message.status.unwrap_or(StatusCode::OK) {
  - StatusCode::TIMEOUT => {
  - return Poll::Ready(None);
  - }
  - StatusCode::IDLE_HEARBEAT => {
  - return std::task::Poll::Pending;
  - }
  - status => Some(status),
  - };
  + Poll::Ready(maybe_message) => match maybe_message {
  + Some(message) => match message.status.unwrap_or(StatusCode::OK) {
  + StatusCode::TIMEOUT => Poll::Ready(None),
  + StatusCode::IDLE_HEARBEAT => Poll::Pending,
  + _ => {
  self.pending_messages -= 1;
  Poll::Ready(Some(Ok(JetStreamMessage {
  context: self.context.clone(),
  message,
  })))
  - } else {
  - Poll::Ready(None)
  - }
  }
  + },
  + None => Poll::Ready(None),
  + },
  std::task::Poll::Pending => std::task::Poll::Pending,
  }
  }
  