align use_list with number of variables during flatten, push clause and bool_vars_of addition into clause and atom creation time.

src/ast/sls/sls_arith_clausal.h

@@ -81,6 +81,7 @@ namespace sls {
         unsigned m_best_last_step = 0;
         unsigned m_num_lookaheads = 0;
         double   m_best_score = 0;
+        unsigned m_num_clauses = 0;
 
         // avoid checking the same updates twice
         var_t m_last_var = UINT_MAX;