Secure Zero plaintext ballot selection values when the finalizer runs

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尚未确定任何文件或测试。首先在 C++ 实现中定位 finalizer 以及明文选票选择值的处理逻辑，然后确定预期的清零行为；完成的标准是 finalization 后无法再恢复这些值，并且相关的安全行为已由测试覆盖。

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