Store DateCache in TLS

[adam-fowler]

Moved DateCache to thread local storage as it is quicker to access than via the EventLoopStorage
Also wrote RFC1123 formatter without using Foundation, so we can move it to Hummingbird

[codecov]

Codecov Report

Merging #56 (5eda422) into main (00dd64f) will increase coverage by 0.11%.
The diff coverage is 98.64%.

@@            Coverage Diff             @@
##             main      #56      +/-   ##
==========================================
+ Coverage   82.96%   83.08%   +0.11%     
==========================================
  Files          47       46       -1     
  Lines        2319     2353      +34     
==========================================
+ Hits         1924     1955      +31     
- Misses        395      398       +3     

Impacted Files	Coverage Δ
Sources/Hummingbird/Utils/HBParser.swift	78.15% <ø> (ø)
Sources/Hummingbird/Application.swift	92.45% <83.33%> (-1.17%)	⬇️
...rces/Hummingbird/Extensions/EventLoopStorage.swift	93.33% <100.00%> (-6.67%)	⬇️
Sources/Hummingbird/Router/RouterMethods.swift	87.50% <100.00%> (ø)
...Hummingbird/Server/Application+HTTPResponder.swift	84.84% <100.00%> (+0.47%)	⬆️
Sources/Hummingbird/Utils/DateCache.swift	100.00% <100.00%> (ø)
...s/HummingbirdFoundation/Utils/DateCache+Date.swift	100.00% <100.00%> (ø)
Sources/HummingbirdXCT/HBXCTLive.swift	90.00% <100.00%> (ø)
... and 1 more

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