feat: Support playback speed and volume shortcuts for shorts

[hkzo]

Summary

This PR adds support for keyboard shortcuts for playback speed and volume on YouTube Shorts.

Ref: #4306

Changes

Previously, keyboard shortcuts for volume and playback speed were scoped primarily to regular watch pages, failing to recognize or apply to YouTube Shorts players.

• Updated volume and playback speed shortcut handlers to correctly detect and resolve the Shorts player and video elements when dataset.pageType === 'shorts'.
• Ensured shortcuts operate seamlessly on both standard watch pages and YouTube Shorts.

Testing

• Verified that volume increase/decrease keyboard shortcuts work correctly on Shorts.
• Verified that playback speed increase/decrease/reset keyboard shortcuts work correctly on Shorts.
• Verified that standard player functionality continues to work correctly without regressions.

Notes

I used AI assistance only for translating this PR description. I made the code changes and performed the testing myself.

[ImprovedTube2]

Thank you very much! @hkzo