To break a potential read/write deadlock, gossipsub uses an unbounded
queue for writes - when peers are too slow to process this queue, it may
end up growing without bounds causing high memory usage.
Here, we introduce a maximum write queue length after which the peer is
disconnected - the queue is generous enough that any "normal" usage
should be fine - writes that are `await`:ed are not affected, only
writes that are launched in an `asyncSpawn` task or similar.
* avoid unnecessary copy of message when there are no send observers
* release message memory earlier in gossipsub
* simplify pubsubpeer logging
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