CronLite In-Memory Scheduler

Design an in-memory task scheduler library. Users should be able to schedule 'Tasks' to run at a specific time, after a delay, or periodically. Tasks can be any block of code. Requirements: 1) Tasks can be canceled or paused, 2) Support for basic retry logic on failure, 3) Limit the number of concurrent tasks running (thread pool management), and 4) Provide hooks for logging task start/completion.