Design a Rate Limiter

Problem

Implement a rate limiter that restricts a user to at most N requests per window of T seconds.

Your class should support:

- `RateLimiter(int maxRequests, int windowSeconds)`

- `boolean allowRequest(String userId)` — returns true if the request is allowed, false if rate limited

Assume a single-machine deployment for now. Requests from the same userId within the window count toward the limit.