Added complete test coverage for the identifier-resolver utility module which provides username/UUID resolution functionality. The test suite includes:
- isUUID validation tests (valid/invalid formats, case sensitivity, edge cases)
- resolveIdentifierToCreator tests (username lookups, UUID fallbacks, error handling)
- resolveIdentifierToUserId tests (optimization paths, resolution logic)
- resolveIdentifierToUsername tests (direct returns, API resolution)
- Integration scenarios (full workflows, mixed case handling)
All 26 tests passing with comprehensive mocking of fetch API calls.
