Use `relnext` and `relprev` for improving data-based synthesis performance

Currently CifBddEdge#apply uses the BDD operations applyEx and replaceWith for determining the set of successor/predecessor states reachable by one forward/backward step of the edge. However, there exist specialized BDD operations, relnext and relprev, for computing successor/predecessor states in a single step, which is more efficient than applying applyEx+replaceWith as two steps. This improves performance of data-based synthesis as well as reduces the maximum number of used BDD nodes.