Retry with backoff

A request to a flaky service fails now and then. Retrying right away usually fails again, so you wait a little, then longer, then longer still. That is exponential backoff.

Implement retry(fn, options). It calls the async function fn and returns a promise.

• options.maxAttempts is the total number of calls to fn, including the first. It defaults to 3.
• options.baseDelay is the wait in milliseconds after the first failure. It defaults to 100.
• The wait doubles after each failure: baseDelay, then twice that, then four times, and so on.
• If a call succeeds, resolve with its result at once.
• If every attempt fails, reject with the error from the last attempt.

fn receives the attempt number, starting at 1.

With maxAttempts of 3 and baseDelay of 100:

const data = await retry((attempt) => fetchProfile(attempt))
// attempt 1 fails, wait 100ms
// attempt 2 fails, wait 200ms
// attempt 3 fails, reject with attempt 3's error. No wait after it.

The grader moves time on a virtual clock. setTimeout and clearTimeout work. Time does not pass on its own, and setInterval is not available.

Requirements:

• A success on the first call makes one call and does not wait.
• After a failure, wait before the next attempt. Each wait is double the one before.
• Stop after maxAttempts calls and reject with the last error.
• Do not wait after the final failed attempt.
• Pass the attempt number to fn.

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