Minimal example for scala/bug#11734

Fails to compile with Scala 2.13, succeeds with 2.12.10. Replacing the wildcard import in one of the files in the motion package solves the problem on 2.13 as well, problematic seems only the cycle between class Velocity extends TimeIntegral[Acceleration] and class Acceleration extends TimeDerivative[Velocity] when both reference each other via a type alias defined in the squants package object.