* Add more comprehensive structs unit-tests
* Make VerifySignatures fail on duplicate addresses
* Adjust duplicate detection to guard on signatures instead of addresses
* Add monotonic check in VerifySignatures
* Move logic into VerifySignatures and add more test cases
* Add a paranoid check for duplicate signers
* Make VerifySignatures unit-tests less contrived
* Add more verify signature test cases
* Refactor VerifySignatures tests
* Add VerifySignature fuzz tests
* Add tc.result checking instead of hardcoded true
* Change comparison so it throws debug on failure for fuzz tests
* Add unit-tests for observation signature logic
* Fix comment typos
* Refactor observation tests
* Add missing test case
* Fix VAAInvalidSignatures test case label
* Clean up unit-tests for observation and structs
* Change errorString convention in test
* Format Signature Verification Test Cases
* Remove unnecessary casting
* Add multi-signer same key cases
* Fix err usage in test cases
* Remove duplicate getVAA
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