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

tests/stress/loop_for_in.js

@@ -0,0 +1,13 @@
+var ITERATIONS = 5000;
+
+var obj = {};
+for (var i = 0; i < 100; i++) {
+  obj["k" + i] = i;
+}
+var sum = 0;
+for (var j = 0; j < ITERATIONS; j++) {
+  for (var k in obj) {
+    sum += obj[k];
+  }
+}
+sum