change zsetxxxxWithScore interfaces from returning Set<Tuple> to List<Tuple> for -
1. saving unnecessary hashCode computation/type conversion for performance, the protocol has guaranteed unique result;
2. LinkedHashSet is not equivalent to a sorted list - LinkedHashSet.equals() doesn't take order into consideration, e.g.,
    LinkedHashSet<Integer>set1 = new LinkedHashSet<Integer>(); set1.add(1); set1.add(4);
    LinkedHashSet<Integer>set2 = new LinkedHashSet<Integer>(); set2.add(4), set2.add(1);
    set1.equals(set2) returns true