this makes using the zero-copy pipes a lot more ergonomic. error
handling is unfortunately not trivial and duplicating it for all
pipe users would thus be a bad idea. we're also not oblivious to
the fact that this is a `sourceToSink`, but it's async this time
around. (at least we don't need terrible stackful coroutines..?)
Change-Id: I1ba59f27183988ad68e7f88d102935d005690f43
eldritch horrors
66090810f1