test(stdlib): 添加ArrayObject的count函数测试用例

- 创建了新的测试文件tests/aot/stdlib/countable.phpt
- 添加ArrayObject实例化和元素添加的测试代码
- 验证count函数对ArrayObject的计数功能
- 设置期望输出为int(3)验证测试结果

tests/aot/stdlib/countable.phpt

@@ -0,0 +1,12 @@
+--TEST--
+count: ArrayObject
+--FILE--
+<?php
+$array = new ArrayObject();
+$array[] = 1;
+$array[] = 2;
+$array[] = 3;
+var_dump(count($array));
+?>
+--EXPECT--
+int(3)