Prevent treating warnings as errors from conflicting in consuming packages

[dfed]

Per #70, turning on .treatAllWarnings(as: .error) in a library causes errors for library consumers since Swift Package Manager suppresses warnings in package dependencies.

We're still enforcing warnings as errors in CI, so we aren't going to introduce warnings into the repo. Unfortunate design decision within SPM, but here we are.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (b30374b) to head (2da42c0).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #71   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           13        13           
  Lines         1301      1301           
=========================================
  Hits          1301      1301           

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