zadd method
Adds member with the specified score to the sorted set stored at key.
Returns 1 if the member was added, 0 if it was updated.
Throws a ValkeyServerException if the key holds a non-sorted-set value.
Implementation
@override
Future<int> zadd(String key, double score, String member) =>
_executeOnKey(key, (client) => client.zadd(key, score, member));