Implement the RecentCounter class which counts the number of recent requests within a time window.

Implement ping(t) that records a new request at time t (where t is strictly increasing across calls) and returns the number of pings that occurred in the inclusive window [t - 3000, t].

This is the classic sliding-window queue pattern — push the new time, pop times that fell out of the window, then the queue size is the answer.

Example: pings [1, 100, 3001, 3002] → [1, 2, 3, 3] (at t = 3002, the window is [2, 3002] so 1 has dropped out).