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

tests/stress/prop_set.js

@@ -0,0 +1,10 @@
+var ITERATIONS = 100000;
+
+var obj = { x: 0, y: 0 };
+var sum = 0;
+for (var i = 0; i < ITERATIONS; i++) {
+  obj.x = i;
+  obj.y = i * 2;
+  sum += obj.x + obj.y;
+}
+sum