subsequence method
Creates a new sequence containing the message IDs/UIDs between start
(inclusive) and end
(exclusive)
Implementation
MessageSequence subsequence(int start, [int? end]) {
final sublist = _ids.sublist(start, end);
final subsequence = MessageSequence(isUidSequence: isUidSequence);
subsequence._ids.addAll(sublist);
return subsequence;
}