fix: improve speed in hilbert transform by FFT

[jobo322]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.39%. Comparing base (165bf0e) to head (74bd954).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #284      +/-   ##
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- Coverage   96.39%   96.39%   -0.01%     
==========================================
  Files         184      184              
  Lines        5164     5161       -3     
  Branches     1151     1150       -1     
==========================================
- Hits         4978     4975       -3     
  Misses        186      186              

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[lpatiny]

If the result is the same and the algorithm is faster this PR is ok for me.

[lpatiny]

@jobo322 why was this PR not merged ? Did you do any benchmark ? Do you know how much faster it is ?

[jobo322]

from the README of fft.js it may run 25% faster, but seems the improvement in speed is not than good as 25 %. at least it avoid the for loop