Fix requireAllExcept runtime error

[Sam-61s]

Summary

Fixes a runtime crash in the requireAllExcept keyword where remove() was called on a generator returned by Browser.keys().

Fix

Convert propertyNames to a Set
Replace invalid remove() call with Set.delete()

-requireAllExcept.forEach((propertyName) => propertyNames.remove(propertyName));
+requireAllExcept.forEach((propertyName) => required.delete(propertyName));

Result

Validation no longer crashes and correctly fails when required properties are missing.

Related Issue

Fixes #99

[jdesrosiers]

Thanks!