feat(contractor/contractor_forall): Make forall contractor thread-safe
feat(contractor/contractor_forall): Make forall contractor thread-safe

dreal/dreal4,dreal/dreal4,soonho-tri/dreal4,soonho-tri/dreal4,dreal/dreal4,soonho-tri/dreal4,dreal/dreal4,soonho-tri/dreal4