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

tests/stress/string_replace.js

@@ -0,0 +1,9 @@
+var ITERATIONS = 20000;
+
+var s = "hello world, hello engine, hello rust";
+var sum = 0;
+for (var i = 0; i < ITERATIONS; i++) {
+  var r = s.replace("hello", "hi");
+  sum += r.length;
+}
+sum