spublish method
Posts a message to the given channel using Sharded Pub/Sub.
Returns the number of clients that received the message.
Note: In Cluster mode, this command is routed to the specific node
that owns the slot for channel.
Implementation
@override
Future<int> spublish(String channel, String message) async {
final response = await execute(['SPUBLISH', channel, message]);
return response as int;
}