Trio-parallel

- The behavior and lifetime of worker processes can now be customized with the `cache_scope` context manager. (19)

- remove `__version__` attribute to avoid crash on import when metadata is unavailable (55)

- `trio_parallel.BrokenWorkerError` now contains a reference to the underlying worker process which can be inspected e.g. to handle specific exit codes. 48

- Workers are now fully synchronized with only pipe/channel-like objects, making it impossible to leak semaphores. 33
- Fix a regression of a rare race condition where idle workers shut down cleanly but appear broken. 43
- Ensure a clean worker shutdown if IPC pipes are closed 51

This should put a sdist and wheel up on test.pypi.org

- Correctly handle the case where `os.cpu_count` returns `None`. [32](https://github.com/richardsheridan/trio-parallel/issues/32)
- Ignore keyboard interrupt (SIGINT) in workers to ensure correct cancellation semantics and clean shutdown on CTRL+C. [35](https://github.com/richardsheridan/trio-parallel/issues/35)

- Fixed an underlying race condition in IPC. Not a critical bugfix, as it should not be triggered in practice. (15)
- Reduce the production of zombie children on Unix systems (20)
- Close internal race condition when waiting for subprocess exit codes on macOS. (23)
- Avoid a race condition leading to deadlocks when a worker process is killed right after receiving work. (25)