How would you design a generic type-safe event emitter in TypeScript that allows subscribing to specific event types and emits them with typed payloads? Consider the ability to handle multiple listeners for each event type and the need to unregister listeners. Discuss the structure and provide example usage.

type Listener<T> = (payload: T) => void; class EventEmitter<T extends Record<string, any>> { private listeners: { [K in keyof T]?: Listener<T[K]>[] } = {}; on<K extends keyof T>(event: K, listener: Listener<T[K]>): void { if (!this.listeners[event]) this.listeners[event] = []; this.listeners[event]!.push(listener); } emit<K extends keyof T>(event: K, payload: T[K]): void { this.listeners[event]?.forEach(listener => listener(payload)); } off<K extends keyof T>(event: K, listener: Listener<T[K]>): void { this.listeners[event] = this.listeners[event]?.filter(l => l !== listener); } } // Example usage: const emitter = new EventEmitter<{ click: { x: number; y: number }; keypress: string }>(); emitter.on('click', (payload) => console.log(`Clicked at ${payload.x}, ${payload.y}`)); emitter.emit('click', { x: 10, y: 20 });