🧪 Add unit test for update_rhythm_from_slider

[dynamikdev]

🎯 What: The testing gap addressed is the lack of unit tests for the update_rhythm_from_slider UI system, which maps slider interaction state to internal rhythm state.
📊 Coverage: The new test suite covers the primary successful state update path (checking RhythmState duration snapping and rounding, HighlightTimer duration updates, and Text string updates) and the early-return path when the slider change is insignificant (< 0.01 threshold).
✨ Result: Test coverage for UI system interactions has improved, creating a more robust safety net against regressions in configuration UI logic.

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PR created automatically by Jules for task 15732534782582082057 started by @dynamikdev

[google-labs-jules]

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