[ATR-24944] Change NavGraph API from std::set to std::vector
Change NavGraph API from std::set to std::vector, as we store pointers, and pointer ordering will change each time we run the code.
Introduce explicit de-duplication to replace the set deduplication.
In the reference, some of the recursive printout is reordered, but the underlying structure of the graph's probed by the unit test are unchanged. As expected.