Fix : ELEMENTS_PER_BLOCK may be incorrect

[shanhe72101]

What problem does this PR solve?

Issue Number:#2561

Problem Summary:

推测常量ELEMENTS_PER_BLOCK本意是一页可以容纳DoublyBufferedData::Wrapper的个数，误写成了sizeof(T)
DoublyBufferedData::Wrapper增加BAIDU_CACHELINE_ALIGNMENT修饰，避免伪共享

What is changed and the side effects?

Changed:

Side effects:

• Performance effects(性能影响):

• Breaking backward compatibility(向后兼容性):

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Check List:

• Please make sure your changes are compilable(请确保你的更改可以通过编译).
• When providing us with a new feature, it is best to add related tests(如果你向我们增加一个新的功能, 请添加相关测试).
• Please follow Contributor Covenant Code of Conduct.(请遵循贡献者准则).

[wwbmmm]

LGTM

[chenBright]

LGTM