You are asked to build an in-memory rate limiter for an API service. For each `user_id`, allow at most `limit` requests during any rolling window of `window_seconds` seconds. Implement a class with the following interface: - `RateLimiter(limit: int, window_seconds: int)` - `allow(user_id: str, timestamp: int, request_id: str | None = None) -> bool` Behavior: 1. Requests arrive in nondecreasing `timestamp` order. 2. A request should be accepted only if the user has made fewer than `limit` accepted requests in the interval `[timestamp - window_seconds + 1, timestamp]`. 3. Requests that fall outside the current sliding window must be removed efficiently. 4. `allow` returns `true` if the current request is accepted and `false` otherwise. Follow-up: if `request_id` is provided, repeated requests with the same `request_id` from the same user within the active window should be treated as duplicates and should not consume additional quota. Explain how you would extend the data structure with a set to support this efficiently.