Service composition syntax with <+> doesn't work for AuthedService

[SystemFw]

Some people have already stumbled upon this in the wild: <+> syntax doesn't work for AuthedService (also referenced in #1501).

The issue boils down to

 type AuthedService[F[_], T] = Kleisli[OptionT[F, ?], AuthedRequest[F, T], Response[F]]

having T on the right, which prevents partial unification from triggering.

Minimisation:

object Gotcha {
  import cats._, data._, implicits._

  implicit def http4sKleisliSemigroupK[F[_]: SemigroupK, A]: SemigroupK[Kleisli[F, A, ?]] =
    new SemigroupK[Kleisli[F, A, ?]] {
      def combineK[B](x: Kleisli[F, A, B], y: Kleisli[F, A, B]) =
        Kleisli(req => x(req) <+> y(req))
    }

  case class Req[F[_]]()
  case class Res[F[_]]()

  type Service[F[_]] = Kleisli[OptionT[F, ?], Req[F], Res[F]]

  def normal[F[_]: Monad](a: Service[F], b: Service[F]) = a <+> b

  case class AuthedReq[F[_], T]()
  type AuthedService[F[_], T] = Kleisli[OptionT[F, ?], AuthedReq[F, T], Res[F]]
  type AuthedServiceSwapped[T, F[_]] = Kleisli[OptionT[F, ?], AuthedReq[F, T], Res[F]]

  // def doesNotCompile[F[_]: Monad, T](a: AuthedService[F, T], b: AuthedService[F, T]) =
  //   a <+> b

  def compiles[F[_]: Monad, T](a: AuthedServiceSwapped[T, F], b: AuthedServiceSwapped[T, F]) =
    a <+> b
}

I'll PR a fix for this asap