Extend counter to per-client rate limiting

You are extending the recent-requests counter to support **per-client** rate limiting. Each request now includes a `clientId` identifying the caller. You must track hits separately for each client, still over the last 5 minutes. Design and implement a class that supports the following operations: - `void hit(String clientId, int timestamp)` Records a hit from `clientId` at time `timestamp` (in seconds). Assumptions: - Timestamps are given in **strictly increasing** order across all calls. - There may be multiple hits from the same or different clients at the same `timestamp`. - `int getHits(String clientId, int timestamp)` Returns the number of hits made by this specific `clientId` in the **past 5 minutes**, i.e., in the inclusive interval `[timestamp - 299, timestamp]`. Additional requirements and constraints: - The system may have **many distinct clients**; most of them will be idle at any given time. - You only need to keep data that is at most 5 minutes old per client; older hits for that client should be discarded or ignored. - Aim for time complexity close to O(1) **amortized** per operation and space proportional to the number of hits in the last 5 minutes. - Your design should be efficient both when there is a single very active client and when there are many moderately active clients. Define the class interface and implement the methods `hit` and `getHits`.