Rate Limiter

Implement a createRateLimiter that limits how many times a function can be called within a time window.

Requirements

• createRateLimiter(fn, maxCalls, windowMs) — return a rate-limited version of fn
• Allow at most maxCalls invocations per windowMs milliseconds
• Calls exceeding the limit should be dropped (return undefined)
• The window is sliding: old calls expire after windowMs

Example

const limited = createRateLimiter(x => x, 2, 100);
limited(1); // 1
limited(2); // 2
limited(3); // undefined (rate limited)
// After 100ms...
limited(4); // 4