CUFFT-related optimizations

[maleadt]

cc @marius311 @vchuravy @DhairyaLGandhi

[codecov]

Codecov Report

Merging #428 into master will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #428      +/-   ##
==========================================
+ Coverage   79.75%   79.78%   +0.02%     
==========================================
  Files         170      170              
  Lines        9051     9063      +12     
==========================================
+ Hits         7219     7231      +12     
  Misses       1832     1832              

Impacted Files	Coverage Δ
lib/cufft/fft.jl	90.49% <100.00%> (+0.54%)	⬆️
src/array.jl	91.23% <100.00%> (ø)

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