feat(widget): add help widget and improve score widget

- Introduced a new `Help` widget to display user instructions.
- Improved the `ScoreListWidget` by removing unnecessary execution rendering methods and simplifying state transitions.
- Cleaned up unused imports and refactored code for better readability.

harmony-rs/harmony_tui/src/widget/mod.rs

@@ -1 +1,2 @@
 pub mod score;
+pub mod help;