Build a rate limiter

An API should let a client send a quick burst of requests, then slow them to a steady rate. A token bucket does that: the bucket holds tokens, each request spends some, and tokens drip back in over time.

Implement createLimiter({ capacity, refillPerSecond }). It returns an object with one method, tryRemove(n).

• The bucket starts full, holding capacity tokens.
• tryRemove(n) returns true and spends n tokens if the bucket holds at least n. Otherwise it returns false and spends nothing.
• n defaults to 1.
• Tokens refill continuously at refillPerSecond, in fractions. Half a second at 2 per second adds 1 token. The bucket never holds more than capacity.

Capacity 3, refilling 1 token per second:

const limiter = createLimiter({ capacity: 3, refillPerSecond: 1 })
limiter.tryRemove(2) // true, 1 token left
limiter.tryRemove(2) // false, nothing spent
// 1 second passes, 2 tokens in the bucket
limiter.tryRemove(2) // true

The grader moves time on a virtual clock. Date.now works. Time does not pass on its own, and setInterval is not available. Read the time when tryRemove is called instead of running a timer.

Requirements:

• A full bucket allows a burst up to capacity.
• A refused request spends no tokens.
• Refill adds up between calls, including fractions of a token.
• The bucket never holds more than capacity.
• A request for more than capacity is always refused.

Write a top-level function named createLimiter. Do not use export or module.exports.