[Behavioral 7] Observer design pattern with TypeScript example

Key Benefits of the Observer Pattern:
- Loose Coupling: The subject and observers are loosely coupled, promoting modularity and flexibility.
- Efficient Notification: Changes are propagated efficiently to all interested observers.
- Scalability: New observers can be added or removed dynamically without affecting existing functionality.
- Reusability: The pattern can be applied to various scenarios, such as event handling, data synchronization, and more.

By understanding and applying the Observer Design Pattern, you can create more flexible, maintainable, and responsive software systems in TypeScript.