use lazy scopes to avoid push/pop overhead

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/smt/smt_quantifier.h

@@ -34,6 +34,9 @@ namespace smt {
     class quantifier_manager {
         struct imp;
         imp *                       m_imp;
+        unsigned                    m_lazy_scopes;
+        bool                        m_lazy;
+        void flush();
     public:
         quantifier_manager(context & ctx, smt_params & fp, params_ref const & p);
         ~quantifier_manager();