Richer types for akka-grpc generated code

GreeterService.scala

trait GreeterService {
  ...  
}

object GreeterService extends GreeterServiceCompanion[GreeterService] {
  override val name = "helloworld.GreeterService"
  ...
}

class GreeterServiceClient(channel: Channel, options: CallOptions)(implicit mat: Materializer, ex: ExecutionContext) extends GreeterService {
  ...
}

object GreeterServiceClient extends GreeterServiceClientCompanion[GreeterService] {
  override def apply(channel: Channel)(implicit mat: Materializer, ex: ExecutionContext): GreeterService = ...
  ...
}

object GreeterServiceHandler extends GreeterServiceHandlerCompanion[GreeterService] {
  // I'm not sure if a PartialFunction is OK or if we want a richer return type for this method too.
  override def apply(implementation: GreeterService)(implicit mat: Materializer): PartialFunction[HttpRequest, Future[HttpResponse]] = {
  ...
}