Create a backpressure controller for a stream. Pass it to one or more
sources you're connecting to, and if they support backpressure they'll
respond when you call its .pause() and .resume() methods.
Optional: a job that controls readiness. (The throttle will
pause indefinitely when the job ends.) Defaults to the currently-active job,
but unlike most such defaults, it won't throw if no job is active.
Create a backpressure controller for a stream. Pass it to one or more sources you're connecting to, and if they support backpressure they'll respond when you call its .pause() and .resume() methods.