Debug a Concurrent Job Scheduler

You are given a buggy Python job scheduler that runs many independent jobs concurrently. Each job has an ID, a callable, a maximum retry count, and a terminal status: succeeded or failed. The scheduler maintains pending, running, completed, and failed job sets; uses worker threads or asynchronous tasks; enforces a rate limit of at most R job starts per second; and records metrics such as job start time, finish time, latency, retry count, and final status. Your task is to debug and improve the scheduler. Address the following: 1. Find possible data races, deadlocks, and lock-contention hot spots. 2. Verify whether the rate limiter is correct under concurrency. 3. Write tests that prove the scheduler works correctly under success, failure, retry, cancellation, and high-concurrency scenarios. 4. Compute the total time needed to schedule a batch of jobs and the final job success rate. 5. Explain what instrumentation or logs you would add to make future debugging easier.