just_audio's playerStateStream is .distinct() over a value-equal
PlayerState, so stopping an already-idle player emits nothing. Paired
with the source-change mask -- which writes loading into playbackState
rather than filtering at read time -- a stop landing before native init
completed would leave the state at loading forever.
audio_service only tears the foreground service down on a non-idle to
idle transition, so that window produced an unkillable notification
stuck on "cargando" with a dead Stop button: strictly worse than the
teardown this branch removes.
Additive and idempotent -- when the player does emit its own idle, this
just lands first.