Feature/improve decodable configuration

[roanutil]

• Improve API for configuring decoder for Option and OptionSet
• Add OptionDecodingTests and OptionSetDecodingTests
• Add helpers for easily adding decode configuration to a decoder's user info dictionary for Option and OptionSet
• Add remaining helpers for configuring a decoder for Option and OptionSet decoding

[codecov]

Codecov Report

Merging #8 (38bdd47) into main (faa43b0) will increase coverage by 4.27%.
The diff coverage is 80.24%.

@@            Coverage Diff             @@
##             main       #8      +/-   ##
==========================================
+ Coverage   77.07%   81.34%   +4.27%     
==========================================
  Files          19       23       +4     
  Lines        1339     1410      +71     
==========================================
+ Hits         1032     1147     +115     
+ Misses        307      263      -44     

Impacted Files	Coverage Δ
...gumentEncoding/DecoderUserInfo+OptionHelpers.swift	50.00% <50.00%> (ø)
...entEncoding/DecoderUserInfo+OptionSetHelpers.swift	53.33% <53.33%> (ø)
Sources/ArgumentEncoding/Option.swift	60.41% <100.00%> (+16.96%)	⬆️
Sources/ArgumentEncoding/OptionSet.swift	63.63% <100.00%> (+31.20%)	⬆️
...ts/ArgumentEncodingTests/OptionDecodingTests.swift	100.00% <100.00%> (ø)
...ArgumentEncodingTests/OptionSetDecodingTests.swift	100.00% <100.00%> (ø)