Improve detection mechanism on Deezer

[guihkx]

Originally posted by @guihkx in https://github.com/guihkx/spotishush/issues/33#issuecomment-1753562150

I guess one way to deal with this in a more "definite" manner, would be by looking for that <audio> element through the entire node subtree of #page_content.

Though I'm certain that would be slower than the current solution, and I'm not sure if it would introduce delay in muting.

Anyway, let me know if you still want to work on this - I'm open to different suggestions too.