Use RealDot.realdot for more efficient real(dot(x, y))

[devmotion]

This PR uses RealDot.realdot to perform computations of real(dot(x, y)) more efficiently. RealDot.jl is a very lightweight package that only defines realdot and only depends on LinearAlgebra: https://github.com/JuliaMath/RealDot.jl/blob/main/src/RealDot.jl

[codecov]

Codecov Report

Merging #355 (2d6a42f) into master (c4b0b83) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #355   +/-   ##
=======================================
  Coverage   93.26%   93.26%           
=======================================
  Files          12       12           
  Lines        2687     2687           
=======================================
  Hits         2506     2506           
  Misses        181      181           

Flag	Coverage Δ
unittests	93.26% <100.00%> (ø)

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Impacted Files	Coverage Δ
src/SpecialFunctions.jl	100.00% <ø> (ø)
src/chainrules.jl	100.00% <100.00%> (ø)

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[stevengj]

I appreciate the thought here, but I'm skeptical that this can possibly matter much here given the cost of evaluating the Bessel functions.