Remove Objective-C support

[dfed]

This is a breaking change. By removing Objective-C support, we can support more Swift platforms.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.05%. Comparing base (ae51200) to head (7af6caf).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #102      +/-   ##
==========================================
+ Coverage   99.02%   99.05%   +0.03%     
==========================================
  Files           8        8              
  Lines         512      529      +17     
==========================================
+ Hits          507      524      +17     
  Misses          5        5              

Files with missing lines	Coverage Δ
Sources/CacheAdvance/CacheAdvance.swift	100.00% <100.00%> (ø)
Sources/CacheAdvance/CacheHeaderHandle.swift	100.00% <100.00%> (ø)
Sources/CacheAdvance/FileHandleExtensions.swift	100.00% <100.00%> (ø)

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