Implement a fully-featured EventEmitter class with on(), off(), emit(), and once() methods. Use private class fields.

Implement a retry function with exponential backoff. It should retry a failed async operation up to N times, doubling the wait time between retries, with optional jitter.

Implement a middleware pipeline similar to Express.js. It should support async middleware functions with next() and error handling middleware.

Implement a TaskQueue class that processes async tasks with a configurable concurrency limit.