Account for SignalOffloader methods throwing when used from operators

[Scottmitch]

[1] For methods that account for EnqueueForOffloadingFailed they should also be accounting for more general exceptions that maybe thrown. For example an exception is thrown if the offloader has already be terminated.
[2] For methods that don't account for EnqueueForOffloadingFailed we need to analyze the callers of the offload methods and make sure they propagate exceptions accordingly. For example in the case of ResumeCompletable we invoke this method from onError which means we likely won't propagate the exception in an orderly fashion if this method throws.

[1] #192 (comment)
[2] #192 (comment)