goodboy/tractor

AI Summary: This task involves enhancing the `tractor` project's error handling and cancellation mechanisms to be more granular and aware of different runtime layers (trio tasks, actors, processes, OS). This includes creating new exception types to represent cancellations originating from various layers, improving the handling of `trio.Cancelled` exceptions, and potentially integrating with OS-level signals for more robust cancellation and failure handling in distributed scenarios. The goal is to improve the reliability, resilience, and predictability of `tractor` applications, especially in distributed settings.