toDotString
Formats a BinaryDecisionDiagram using Graphviz DOT notation (https://graphviz.org/). This provides a fast and widely supported solution to visualize the contents of a BDD.
Return
a Graphviz DOT digraph representation of this diagram, with terminal nodes labelled 0/1 and every distinct variable node rendered once (nodes sharing the same value/low/high triple are folded together).
Throws
if the traversal fails.