Optimize PerceptualHash implementation

[jaden-young]

Use System.Numerics to optimize the runtime of PerceptualHash.

For the most part this work was done by @jessetrana at our mutual $DAYJOB, I'm just doing the upstreaming here.

I tried my hand at a similar implementation for AverageHash but didn't see any gains.

Benchmarks

Benchmark code is available at simd-optimization-bench. The test suite is a set of 97 images from Unsplash. The benchmark is measuring the time taken to hash the entire set.

Perceptual Hash

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19043
Intel Core i7-4790K CPU 4.00GHz (Haswell), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=5.0.402
  [Host]     : .NET Core 5.0.11 (CoreCLR 5.0.1121.47308, CoreFX 5.0.1121.47308), X64 RyuJIT
  DefaultJob : .NET Core 5.0.11 (CoreCLR 5.0.1121.47308, CoreFX 5.0.1121.47308), X64 RyuJIT

Method	Mean	Error	StdDev	Ratio
PerceptualHash	656.86 ms	1.515 ms	1.343 ms	1.00
PerceptualHashOptimized	37.38 ms	0.411 ms	0.385 ms	0.06

All Algorithms

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19043
Intel Core i7-4790K CPU 4.00GHz (Haswell), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=5.0.402
  [Host]     : .NET Core 5.0.11 (CoreCLR 5.0.1121.47308, CoreFX 5.0.1121.47308), X64 RyuJIT
  DefaultJob : .NET Core 5.0.11 (CoreCLR 5.0.1121.47308, CoreFX 5.0.1121.47308), X64 RyuJIT

Method	Mean	Error	StdDev	Ratio	RatioSD
DifferenceHash	275.3 μs	1.14 μs	1.01 μs	1.00	0.00
AverageHash	284.2 μs	4.52 μs	4.64 μs	1.03	0.02
PerceptualHashOptimized	36,893.8 μs	142.67 μs	133.45 μs	133.96	0.49
PerceptualHash	656,367.7 μs	1,807.57 μs	1,509.40 μs	2,383.89	11.21

[codecov]

Codecov Report

Merging #36 (d4369c2) into develop (715fa98) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##           develop       #36   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            5         5           
  Lines          155       192   +37     
  Branches        42        12   -30     
=========================================
+ Hits           155       192   +37     

Impacted Files	Coverage Δ
src/ImageHash/HashAlgorithms/PerceptualHash.cs	100.00% <100.00%> (ø)

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[coenm]

@jaden-young , @jessetrana Thanks for your PR.