Implemented FFT convolution and lazy segment tree — fast and efficient

[jsjgdh]

Added implementation of FFT (Cooley–Tukey) for polynomial convolution. Also added a segment tree with lazy propagation for range updates and queries. I have included test for both and also tested it locally on my machine .

[codecov-commenter]

Codecov Report

:x: Patch coverage is 98.16514% with 6 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 86.11%. Comparing base (08d8c6b) to head (a1f9075).

Files with missing lines	Patch %	Lines
Maths/FFT.js	97.36%	4 Missing :warning:
Trees/SegmentTree.js	97.26%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1848      +/-   ##
==========================================
+ Coverage   85.91%   86.11%   +0.19%     
==========================================
  Files         379      382       +3     
  Lines       19778    20105     +327     
  Branches     3015     3085      +70     
==========================================
+ Hits        16993    17314     +321     
- Misses       2785     2791       +6     

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