feat: Modify `positive_fft` function

[Kangwhi-Kim]

close #65

Summary

Write the summary about this PR.

• Modify positive_fft function

Changes

Write changes in detail.

• Change the n-dimensional array operation to be possible. (n = 1, 2, ...)

How to Test?

Write a way to test the changes.

• python test_fft.py

Checklist

• [ ] Do you pass all the tests?
• [ ] Do you write the changes on document such as README?

[Kangwhi-Kim]

deep learning input 넣을 때 n차원 array 연산이 필요하다는 요청에 따라 변경하게 되었습니다.