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

tests/stress/ic_polymorphic.js

@@ -0,0 +1,11 @@
+var ITERATIONS = 100000;
+
+var a = { x: 1, y: 2, z: 3 };
+var b = { x: 4, y: 5, z: 6 };
+var c = { x: 7, y: 8, z: 9 };
+var sum = 0;
+for (var i = 0; i < ITERATIONS; i++) {
+  var t = (i % 3 === 0) ? a : (i % 3 === 1) ? b : c;
+  sum += t.x + t.y + t.z;
+}
+sum