Small Anki addon to adjust the volume of card audio.

Frankly I think this addon is probably better, it just happened to be created between the time I decided to write this addon and the time I actually got to writing it. Also it hasn't been updated for Qt6 yet, while this one has.

For now it's only tested with mpv on Linux for Anki >= 23.10. If you run into problems on another platform, please open an issue and I'll see what I can do.