Make boolean config validator more efficient

[bachya]

Describe what the PR does:

• Don’t recalculate what strings are truthy/falsey every time the validator is called.
• Use sets for slightly faster inclusion checks.

Does this fix a specific issue?

N/A

Checklist:

• Confirm that one or more new tests are written for the new functionality.
• Run tests and ensure everything passes (with 100% test coverage).
• Update README.md with any new documentation.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (5aad471) 100.00% compared to head (1541749) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##               dev      #855   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           32        32           
  Lines         1734      1736    +2     
=========================================
+ Hits          1734      1736    +2     

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