Refactor callbacks to avoid extra binder calls

Main changes are:
- Update metadata when it changes instead of checking in the timer
- Reuse PlaybackState object when checking if media is seekable

Fixes: 132941962
Test: manual, atest com.android.systemui.statusbar.notification.row.wrapper.NotificationMediaTemplateViewWrapperTest
Change-Id: If870159662bdd6d2288c61d80a14060a4e751da7