🧪 Add test for sync_rhythm_ui

[dynamikdev]

🎯 What: Added a missing unit test for the sync_rhythm_ui system in src/logic.rs.
📊 Coverage: The test covers the scenario where the RhythmState duration changes, verifying that the text UI correctly updates to reflect the new time ("Rhythm: {:.1}s") and that the slider entity receives the correct SliderValue.
✨ Result: Improved test coverage and reliability for UI synchronization, ensuring that any future changes to rhythm logic or UI components don't introduce regressions.

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PR created automatically by Jules for task 6348289588112509902 started by @dynamikdev

[google-labs-jules]

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