⚡ Bolt: Use Cached Metadata to Avoid UI Rendering Allocations

[juntaochi]

💡 What: Modified draw_metadata and draw_progress in src/ui/mod.rs to consume strings (Cow<'_, str>) directly from the application's metadata_cache (populated every ~500ms in App::update), instead of dynamically allocating strings like track.name.to_uppercase() and format!("{}/{}", ...) on every TUI frame.

🎯 Why: TUI applications re-render extremely frequently (typically at 60fps or when animated). Doing repeated heap string allocations (.to_uppercase() and format!) inside the hot draw path causes unnecessary memory churn and processing overhead. The string data only needs recalculation when the track identity or playback position actually changes, which is already handled efficiently in the background update loop.

📊 Impact: Significantly reduces heap allocations per frame by avoiding redundant formatting and casing logic. Ensures smoother animations (like text scrolling and throbbers) by removing garbage collection pressure.

🔬 Measurement: Verification passes cargo clippy -- -D warnings and cargo test. Rendering tests continue to function seamlessly as the implementation gracefully falls back to dynamic allocations (Cow::Owned) if the cache is omitted (e.g. in test mock environments).

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PR created automatically by Jules for task 1017169362803392720 started by @juntaochi

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