test(amazonq): add unit tests for authUtil

[opieter-aws]

Problem

There are no unit tests for the new AuthUtil on Flare LSP

Solution

• Add unit test for core AuthUtil functionality
• Create a test util for all tests where AuthUtil is needed
• Ensure all tests that interact with the AuthUtil consume the new test util
• Add destroy method to the AuthUtil class to simplify cleanup for unit tests

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• Treat all work as PUBLIC. Private feature/x branches will not be squash-merged at release time.
• Your code changes must meet the guidelines in CONTRIBUTING.md.
• License: I confirm that my contribution is made under the terms of the Apache 2.0 license.