[UseCase] Segmented Watchlist Flow

[mukesh-5059]

Difficulty: Hard
Location: app/src/main/java/com/example/movies_db/domain/usecase/GetWatchlistUseCase.kt
Description:
The UseCase should expose a specific API for the UI.

• Instead of returning one list, it might need to return a wrapper object WatchlistData(released: List<Movie>, upcoming: List<Movie>) or offer two separate Flow functions.
• Ensure efficient SQL streaming (don't re-query everything if only one item changes).