🧪 test: improve edge case coverage for invalid update values

[johnstrand]

🎯 What: Added a missing edge case test for the store.update function when receiving invalid values.
📊 Coverage: Now validates that calling store.update(null) or store.update("string") does not unintentionally mutate state.
✨ Result: Improved test coverage and reliability for state updates via Squawk.update.

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PR created automatically by Jules for task 8338251468620585122 started by @johnstrand

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