handle singleton domains when converting jtlv output to graph
handle singleton domains when converting jtlv output to graph

because slugs.compiler.convert_to_slugsin drops variables with singleton domains. So these variables will be missing from the variable valuations of the synthesized strategy, not because of a bug in slugs, but because they can only take a fixed value.
necozay/tulip-control,necozay/tulip-control,necozay/tulip-control,necozay/tulip-control,tulip-control/tulip-control,tulip-control/tulip-control,necozay/tulip-control,tulip-control/tulip-control,tulip-control/tulip-control