Refactored caption observation to accept a target class name, making the translator logic easier to reuse for different DOM targets.

This change abstracts the hardcoded player-timedtext selector out of setupObserver and passes the class name in as a parameter instead. It also updates the retry and logging paths so the observer setup is consistently scoped to whatever target class is being watched. The behavior stays the same for current Netflix captions, but the code is now cleaner and easier to adapt if the caption container changes or additional targets need to be supported later.