Build a task scheduler with priorities and retries

• schedule(task, options) accepts a task function and options for priority (higher runs first), delay (run after N ms), and recurring (run every N ms), and returns a task id
• A worker pool with a configurable concurrency limit executes tasks; never more than N run at the same time; ties in priority run in submission order (FIFO)
• A priority queue holds ready tasks; delayed and recurring tasks wait until their time, driven by a single timer pointed at the earliest due task rather than one timer per task
• Retries with exponential backoff and jitter: a failing task is retried up to maxRetries times, then marked failed and reported to an onFailed callback; task timeout support
• cancel(id) stops a queued or recurring task from running again; a running task can be signalled through an AbortSignal
• stop() drains gracefully: no new tasks start, running ones finish (with a timeout), and timers are cleared; status(id) returns queued, running, succeeded, failed or cancelled
• Time comes from an injectable clock and timer so the scheduler is testable without real waiting

Only after every requirement works.

• Persist tasks so they survive a restart
• Per-task rate limits or dependencies between tasks
• Metrics and an event emitter for task lifecycle