Network requests can fail. Good code retries with exponential backoff: waiting longer between each attempt. This is production-grade resilience!

Your Task:

• Create retryWithBackoff(fn, retries, delay)
• fn is an async function that might fail
• Retry up to retries times
• Wait delay ms, then delay * 2, then delay * 4...
• Return result on success, throw after all retries fail