a simple example of how to define a custom shape with 2 inlets and 3 outlets.
case class TwoThreeShape[-In1, -In2, +Out1, +Out2, +Out3](
in1: Inlet[In1@uncheckedVariance],
in2: Inlet[In2@uncheckedVariance],
out1: Outlet[Out1@uncheckedVariance],
out2: Ou...
