Log Message:
py-ipyparallel: updated to 8.4.0

8.4.0 is a small release, with some bugfixes and improvements to the release process.

Bugfixes:

- (`%px`) only skip redisplay of streamed errors if outputs are complete

Compatibility improvements:

- Avoid use of recently deprecated asyncio/tornado APIs
  around 'current' event loops that are not running.

Build improvements:

- Switch to hatch backend for packaging