ExoPlayer initialization should happen in background

[TimoPtr]

Based on https://github.com/home-assistant/android/pull/5840#issuecomment-3547132097 we should make sure that the initialization of the player happens outside of the main thread, it is easy to spot now. Start the dev playground and open the demo player activity in the minimal flavor StrictMode is going to crash the app.

It should be pretty straightforward to fix.