feat: 拆分 stress benchmark 到细粒度单热点测试并修复 bench 采样逻辑

tests/stress/array_for_each.js

@@ -0,0 +1,11 @@
+var ITERATIONS = 2000;
+
+var base = [];
+for (var i = 0; i < 100; i++) {
+  base.push(i);
+}
+var sum = 0;
+for (var j = 0; j < ITERATIONS; j++) {
+  base.forEach(function (x) { sum += x; });
+}
+sum