添加 ffts 库

[XinranSix]

你在什么场景下需要该功能？

快速实现傅里叶变换

描述可能的解决方案

这是该库地址：https://github.com/linkotec/ffts

描述你认为的候选方案

No response

其他信息

No response

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Title: Add ffts library

In what scenario do you need this function?

Quickly implement Fourier transform

Describe possible solutions

This is the library address: https://github.com/linkotec/ffts

Describe your alternatives

No response

Other information

No response

[waruqi]

可以直接来个 pr 过来

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You can send a PR directly.