Allow pickling of AsyncResults

If we pickled AsyncResult objects with:

1. msg_ids
2. client connection info
3. partition info for AsyncMapResults

We could unpickle to an AsyncHubResult with a new client connection, making the workflow of [following past tasks](https://github.com/ipython/ipyparallel/issues/629#issuecomment-966392478) a lot nicer.

Start by tracing AsyncResult and AsyncMapResults, focusing on their message IDs, client connection information, and partition information. Determine how an unpickled result could become an AsyncHubResult with a new client connection; done means these result objects can be pickled and later restored for following past tasks.

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