String == String does not work with embedded NUL characters

https://github.com/arduino/ArduinoCore-API/blob/7f8de5869ee3de7a915bf1db64313c08595b3ac3/api/String.cpp#L445 and https://github.com/arduino/ArduinoCore-API/blob/7f8de5869ee3de7a915bf1db64313c08595b3ac3/api/String.cpp#L445 should use ``memcmp()`` to make sure that a String object can be compared to another String object that has embedded ``NUL`` characters

从 api/String.cpp 中第 445 行附近的比较代码开始，检查存在嵌入式 NUL 字符时 String 对象是如何进行比较的。按照描述更新比较逻辑以处理这些字符，然后验证针对嵌入式 NUL 值的 String-to-String 比较能够正确工作。

由索引模型根据 Issue 内容生成。