nits and use saturating_add for cost

src/extract.rs

@@ -193,21 +193,4 @@ impl<'a> Extractor<'a> {
             }
         }
     }
-
-    pub(crate) fn value_cost(
-        &self,
-        sort: &ArcSort,
-        value: &Value,
-        termdag: &mut TermDag, // it does not make a lot sense to pass termdag since
-                               // we are not returning any term. But to get the cost of
-                               // we have to construct the term first.
-    ) -> Option<usize> {
-        if sort.is_eq_sort() {
-            let id = self.egraph.find(Id::from(value.bits as usize));
-            let (cost, _node) = &self.costs.get(&id)?;
-            Some(*cost)
-        } else {
-            Some(sort.extract_expr(self.egraph, *value, self, termdag)?.0)
-        }
-    }
 }

src/sort/set.rs

@@ -147,10 +147,10 @@ impl Sort for SetSort {
     ) -> Option<(Cost, Expr)> {
         let set = ValueSet::load(self, &value);
         let mut expr = Expr::call("set-empty", []);
-        let mut cost = 0;
+        let mut cost = 0usize;
         for e in set.iter().rev() {
             let e = extractor.find_best(*e, termdag, &self.element)?;
-            cost += e.0;
+            cost = cost.saturating_add(e.0);
             expr = Expr::call("set-insert", [expr, termdag.term_to_expr(&e.1)])
         }
         Some((cost, expr))