Transition from `CompositeError` to builtin `ExceptionGroup`

[PEP-654](https://peps.python.org/pep-0654/) adds a new builtin `ExceptionGroup` type to Python, and `except*` syntax for cleanly handling multiple errors. [The backport](https://pypi.org/project/exceptiongroup/) is already widely used, including by Pytest, Trio, Hypothesis, and many others. I'd love to see `ipyparallel` join in, so that all our users get interoperable tooling and - once they're on recent versions of Python - nice syntax too.

Logistically, this is a substantial lift, but following e.g. https://github.com/python-trio/trio/pull/2213 will hopefully be a lot easier than doing the whole thing from scratch. You might even choose to wait a while for the ecosystem to mature, but I thought it was worth opening an issue now - if nothing else, it's relevant to any _other_ proposed changes to `CompositeError` - and I'm confident that switching over will be the best way forward within the next few years.

Start by reviewing ipyparallel's CompositeError implementation and the linked Python Trio transition described in the issue, along with PEP 654 and the exceptiongroup backport. Done means ipyparallel uses interoperable builtin ExceptionGroup behavior while preserving its existing multiple-error handling.

Escrita pelo modelo de indexação a partir do texto da issue.