Swift settings, clean up storage protocols

[adam-fowler]

• Swift settings ExistentialAny, InternalImportsByDefault, MemberImportVisibility
• Only require RangeReplaceableCollection on Bytes for MemoryBuffer writing functions
• Only conform ZipMemoryStorage to ZipWriteableStorage in Bytes conforms to RangeReplaceableCollection
• Break out ZipReadableStorage and ZipWriteableStorage into separate files

[codecov]

Codecov Report

❌ Patch coverage is 76.38889% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.71%. Comparing base (ea58333) to head (570ebdf).

Files with missing lines	Patch %	Lines
Sources/ZipArchive/ZipReadableStorage.swift	69.23%	8 Missing ⚠️
Sources/ZipArchive/MemoryBuffer.swift	76.19%	5 Missing ⚠️
Sources/ZipArchive/ZipWriteableStorage.swift	75.00%	3 Missing ⚠️
Sources/ZipArchive/ZipMemoryStorage.swift	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #16      +/-   ##
==========================================
- Coverage   86.04%   85.71%   -0.33%     
==========================================
  Files          15       17       +2     
  Lines        1225     1225              
==========================================
- Hits         1054     1050       -4     
- Misses        171      175       +4     

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