src: make BaseObject iteration order deterministic
Previously we just rely on the unordered_set order to iterate over the BaseObjects, which is not deterministic.
The iteration is only used in printing, verification, and snapshot generation. In the first two cases the performance overhead of sorting does not matter because they are only used for debugging. In the last case the determinism is more important than the trivial overhead of sorting. So this patch makes the iteration deterministic by sorting the set first, as what is already being done when we drain the queue.