fix(defineShortcuts): improve chained shortcuts and add test coverage

[al1maher]

🔗 Linked issue

Resolves #5654

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This PR introduces two improvements to the defineShortcuts composable:

1. Chained shortcut handling:

   • Chained shortcuts (e.g., 'f-h') now properly override single key shortcuts when the same keys are used both individually and in a sequence.
   • This ensures that pressing 'f' followed quickly by 'h' triggers 'f-h', while pressing 'f' alone still triggers the single key handler.

2. Test coverage:

   • Adds a comprehensive test suite covering single keys, key chains, and layout-independent mode.
   • Ensures correct behavior across different keyboard layouts and prevents regressions in chained key handling.

Future work may include tests for modifier keys (Ctrl, Shift, Meta) and more complex combinations.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[pkg-pr-new]

npm i https://pkg.pr.new/@nuxt/ui@5747

commit: e503ab7