Add option to force VP09 video codec

[RF1705]

Summary

• add a settings option to force VP09 video playback
• filter non-VP09 video formats from player responses when VP09 is available
• report AV1 as unsupported through browser media capability checks while VP09 forcing is enabled
• pass a VP9 format id into quality selection when possible

Notes

This is intended as an opt-in codec preference for devices where VP09 is preferred over AV1. It does not claim to fix every playback interruption issue, but it gives users a direct switch to avoid AV1 selection.

Testing

• pnpm exec prettier --check src/video-codec.ts src/userScript.ts src/video-quality.ts src/player_api/yt-api.ts
• pnpm run lint:tsc
• pnpm run build
• pnpm run package