⚡ Bolt: [performance improvement] avoid intermediate String allocations for track duration formatting

[juntaochi]

💡 What:
Replaced the format_duration and format_duration_seconds helper functions with newtype wrappers (DisplayDuration and DisplayDurationSeconds) that implement std::fmt::Display.

🎯 Why:
The original functions allocated a String (e.g., "03:45" or "225s") which was then immediately passed into another format! macro during the UI loop. This caused unnecessary intermediate heap allocations on every render tick for the progress bar and metadata sections.

📊 Impact:
Eliminates 8 redundant String heap allocations per tick in src/ui/mod.rs (draw_progress and metadata caching). By utilizing std::fmt::Display, formatting is written directly to the outer buffer, providing a zero-cost abstraction without sacrificing readability.

🔬 Measurement:
Run cargo clippy -- -D warnings and cargo test to verify behavior remains completely identical while avoiding allocations. Benchmark of the Display pattern via independent rustc test verifies identical output format.

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PR created automatically by Jules for task 2197866325734240190 started by @juntaochi

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