Convert test_infer_hypothetical to a non-CI test.
Convert test_infer_hypothetical to a non-CI test.

Using cgpm_metamodel.set_multiprocess(False) and 1 model saves
~40 seconds of runtime without compromising the test case, so we
can now run it as part of the test suite.

Also provides coverage for cgpm_metamodel.CGPM_Metamodel.set_multiprocess

probcomp/bayeslite,probcomp/bayeslite