The ActorProducer is an actor-based Publisher which runs a thunk of code
until Stop is thrown. This means that completion is only signaled if
demand is present for one more element, which makes sense and it legal
according to the wording of the spec. The TCK was too strict in this
regard and has been relaxed.
Things would have “worked” without the relaxation if I had not also
fixed the output buffer management. SubscriptionManagement in
collaboration with the ResizableMultiReaderRingBuffer previously
generated demand on its own, acting like a true buffer. This is
undesired since we want to auto-tune the input buffers, which would get
a lot more complicated and instable with autonomously buffering output
stages in the mix.
Removing this extra-buffering uncovered several places in the test suite
which implicitly relied on this, which were fixed as well.
