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

tests/stress/map_ops.js

@@ -0,0 +1,11 @@
+var ITERATIONS = 50000;
+
+var sum = 0;
+for (var i = 0; i < ITERATIONS; i++) {
+  var m = new Map();
+  for (var j = 0; j < 10; j++) {
+    m.set(j, j * 2);
+  }
+  sum += m.get(5);
+}
+sum