Implement a typed EventEmitter from scratch and explain how the observer and pub/sub patterns differ — including memory-leak risks from forgotten subscriptions.

Imagine you have a toy that makes a sound when you press a button. The observer pattern is like telling your friend to watch the toy and shout when it beeps. The pub/sub pattern is like having a walkie-talkie: you shout a message into it, and anyone listening hears it. If you forget to tell your friend to stop watching, they might keep shouting forever and that's a memory leak!