Separate cache hash length and folder depth

[ronaldbarendse]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
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• I have provided test coverage for my change (where applicable)

Description

As discussed in #210, this separates the cache hash length and (PhysicalFileSystemCache specific) cache folder depth. It also generates shorter cache file names by default by not repeating the characters that are already used in the nested folders.

[codecov]

Codecov Report

Merging #212 (ff55d06) into master (fe0b4e9) will increase coverage by 2%.
The diff coverage is 96%.

@@          Coverage Diff           @@
##           master   #212    +/-   ##
======================================
+ Coverage      86%    89%    +2%     
======================================
  Files          68     65     -3     
  Lines        1791   1653   -138     
  Branches      262    232    -30     
======================================
- Hits         1556   1482    -74     
+ Misses        167    112    -55     
+ Partials       68     59     -9     

Flag	Coverage Δ
unittests	89% <96%> (+2%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
.../ImageSharp.Web/Caching/PhysicalFileSystemCache.cs	97% <95%> (+<1%)	⬆️
...harp.Web/Caching/PhysicalFileSystemCacheOptions.cs	100% <100%> (ø)
src/ImageSharp.Web/Caching/SHA256CacheHash.cs	100% <100%> (ø)
...DependencyInjection/ServiceCollectionExtensions.cs	100% <100%> (ø)
.../ImageSharp.Web/Middleware/ImageSharpMiddleware.cs	85% <100%> (ø)
...harp.Web/Middleware/ImageSharpMiddlewareOptions.cs	90% <100%> (ø)
...ching/LruCache/ConcurrentTLruCache{TKey,TValue}.cs
...hing/LruCache/LongTickCountLruItem{TKey,TValue}.cs
...ching/LruCache/TLruLongTicksPolicy{TKey,TValue}.cs

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[ronaldbarendse]

I've excluded the LRU cache from code coverage for now: I'm not sure why the coverage decreased, but it's completely missing dedicated tests to begin with.

[JimBobSquarePants]

@ronaldbarendse Don't worry about the coverage and don't hide it. It's flaky as hell. I had a change recently observed when converting to png's to LFS pointers

[ronaldbarendse]

Because I think adding a setting just for backwards compatibility isn't the best way forward, I thought about creating a sub-class called LegacyV1PhysicalFileSystemCache (similar naming as the LegacyV1CacheKey). This could then simply set the base class useLegacyName boolean using a protected constructor. But even this introduces code that needs to be cleaned up in the future, so I decided on using the fact that the cache depth and hash length are currently the same to revert back to creating the legacy/longer file paths: #213.

[JimBobSquarePants]

I think closing this PR and opening another was a bit premature. Best leaving those kinds of decisions to the library owners.

[ronaldbarendse]

Fair enough, although I was pretty sure the other PR that doesn't require additional settings would be preferred 😇