Biolinkml Performance Issue #54

The biolinkml biolink-model evaluator takes a loooong time to complete, even in a simple test. This is due to the pattern:

<C> CLOSED {
    (  $<C_tes> (  &<B_tes> ;
          rdf:type [ <t1> ] ?
       ) ;
       rdf:type [ <t2> ]
    )
}

which, in certain situations, can cause the evaulator to take off on a combinatorial explosion