subscribe method
Subscribe a new query set. Returns the assigned querySetId.
Awaits the matching SubscribeApplied so initial rows are in the cache.
Implementation
Future<int> subscribe(List<String> queries) async {
final querySetId = _nextQuerySetId++;
_subscriptionsByQuerySetId[querySetId] = List.of(queries);
final message = SubscribeMessage(queries, querySetId: querySetId);
_connection.send(message.encode());
await onSubscribeApplied.firstWhere((m) => m.querySetId == querySetId);
return querySetId;
}