Add bdd_relprod, bdd_relnext and bdd_relprev with read-once once.

[SSoelvsten]

The bdd_relprod, bdd_relnext, and bdd_relprev functions lack a generator-based overload.

• Add bdd_relprod with a generator<bdd::label_type>.
• Add bdd_replace with a generator<pair<bdd::label_type, bdd::label_type>>.
  • Add bdd_relnext with a generator<pair<bdd::label_type, bdd::label_type>>.
  • Add bdd_relprev with a generator<pair<bdd::label_type, bdd::label_type>>.

The pruning optimisation (or any other) cannot be applied in any of these versions above. It neither seems possible to infer the type of the relabelling. Maybe one should instead "load" the entire set of levels (maybe intersected with its support), to then infer the relabelling mode, and then maybe turn it into a predicate?