Set MediaCodec KEY_PRIORITY to real-time (0)

Refs <https://developer.android.com/reference/android/media/MediaFormat#KEY_PRIORITY>
Refs #6238 comment <https://github.com/Genymobile/scrcpy/issues/6238#issuecomment-3828402687>
PR #6670 <https://github.com/Genymobile/scrcpy/pull/6670>