Various Code Quality Fixes

[JimBobSquarePants]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following matches the existing coding patterns and practice as demonstrated in the repository. These follow strict Stylecop rules 👮.
• I have provided test coverage for my change (where applicable)

Description

I gave the library a bit of a read through to get things ready for a V1.

• Fixes solution so tests and benchmarks run again.
• Fix UTC datetime bug in cache check.
• Remove unnecessary stream copy.
• Reduce allocations for string generation when caching.
• Use async stream dispose.

[JimBobSquarePants]

Thanks @tocsoft

I just need to fix up the integration tests to handle the build output location then I’ll merge it.

[codecov]

Codecov Report

Merging #105 into master will increase coverage by 0.10%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master     #105      +/-   ##
==========================================
+ Coverage   77.08%   77.19%   +0.10%     
==========================================
  Files          46       46              
  Lines        1292     1324      +32     
  Branches      207      211       +4     
==========================================
+ Hits          996     1022      +26     
- Misses        234      238       +4     
- Partials       62       64       +2     

Flag	Coverage Δ
#unittests	77.19% <83.33%> (+0.10%)	⬆️

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Impacted Files	Coverage Δ
...s.Azure/Resolvers/AzureBlobStorageImageResolver.cs	90.00% <ø> (ø)
.../ImageSharp.Web/Middleware/ImageSharpMiddleware.cs	72.48% <50.00%> (-0.81%)	⬇️
src/ImageSharp.Web/Caching/CacheHash.cs	76.47% <60.00%> (-15.84%)	⬇️
.../ImageSharp.Web/Caching/PhysicalFileSystemCache.cs	94.28% <95.83%> (+0.40%)	⬆️
src/ImageSharp.Web/Caching/HexEncoder.cs	100.00% <100.00%> (ø)

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