Further optimization of unit collection and iterator classes. I moved active iterator to a fixed length array slot based system. We currently never peak over 3 concurrrent iterators on a given list so i set it to 5. By having a fixed length array, we drastically improve speed of looking up other active iterator positions and thus we're able to avoid keeping lists of null holder positions. a unit collection should only ever return NULL when at the end of the list. I also optimized = operator