SADDEX key seconds member [member ...]
Time complexity: O(1) for each element added, so O(N) to add N elements when the command is called with multiple arguments.
Warning: Experimental! Dragonfly specific.
Simimar to SADD but adds one or more members that expire after specified number of seconds.
An error is returned when the value stored at
key is not a set.
Integer reply: the number of elements that were added to the set, not including all the elements already present in the set.
dragonfly> SADDEX myset 10 "Hello"
dragonfly> SADDEX myset 20 World Dragonfly
dragonfly> SMEMBERS myset