Design out-of-order windowed stream processor

##### Question Design an event processor for an unbounded, infinite stream of events. Each event has the fields `id`, `timestamp`, `payload` (a string), and `checksum`. Events may arrive out of timestamp order, and they should drive a rolling aggregate over a 1-minute (60-second) sliding window. Your processor must: 1. **Validate each event by its checksum** and discard any event whose checksum does not match its payload. 2. **Drop late and out-of-window events** — any valid event whose timestamp falls more than 60 seconds behind the current window (the latest observed timestamp) is discarded. 3. **Handle duplicates** — if the same event `id` is seen more than once, it must only be counted once. 4. **Maintain and report the average payload length over the latest 60 seconds**, updating continuously as new events arrive and as old events fall out of the window. 5. Keep the **overall time complexity no worse than O(n log n)** across `n` events. Describe the data structures you would use, how you keep the window current as the clock advances, and how you handle late arrivals and duplicates.