hkeys method
Returns all field names in the hash stored at key.
List of fields in the hash, or an empty list when key does not exist.
Implementation
Future<List<String>> hkeys(String key) async {
  final result = (await tier1.hkeys(key)).toArray().payload;
  if (result != null) {
    return result.map((e) => e.toBulkString().payload!).toList(growable: false);
  }
  return [];
}