[core][compiled graphs] Throw unrecoverable actor exceptions at ray.get()

[ruisearch42]

Why are these changes needed?

This PR supports throwing unrecoverable actor exceptions at ray.get(), instead of throwing RayChannelError which was not informative of the actual error. It works by getting and checking the exception from the actor task refs when CompiledDAGRef.get() is about to throw a RayChannelError.

Related issue number

Closes #47790

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    method in Tune, I've added it in doc/source/tune/api/ under the
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• Testing Strategy
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