Extend `dd_reorder` to Multiple Decision Diagrams

[SSoelvsten]

In #560 we add the dd_reorder operation to do dynamic variable reordering on a single decision diagram. Yet, the end-user may want to optimise a few decision diagrams collectively (e.g. multiple transitions relations and the set of states). Luckily, the heuristic search can be extended to be evaluated on the resulting sizes of multiple diagrams. To make it run faster, one may want to only sample a subset of the diagrams (primarily focused on the large ones).