enhance findFactorsBetweenNaive, add testing

[dehann]

see function introduced in #486. Main issue is using ShortestPaths interface of the underlying DFG technology layer, or as generic for non-LightDFGs perhaps copy a local LightSummaryDFG and search for shortest paths there.

[dehann]

This function might also be useful to buildSubgraph method as way to discover all shortest paths between variables given for desired subgraph.