Mapping non-unary higher kinded types to unary higher kinded types to deal with https://youtrack.jetbrains.com/issue/SCL-12892

HKT_Helpers.scala

//works with Kleisli/ReaderT
implicit class NestedToUnary[F[_[_], _, _], G[_], I, O](private val value: F[G, I, O]) extends AnyVal {
  type H[A] = F[G, I, A]
  def unaryKind: H[O] = value
}

//works with fs2.Stream, Free/AuthedService from http4s
implicit class NestedToUnary2[F[_[_], _], G[_], I](private val value: F[G, I]) extends AnyVal {
  type H[A] = F[G, I]
  def unaryKind: H[O] = value
}

//works with Either, Validated
implicit class BinaryToUnary[F[_, _], A, B](private val value: F[A, B]) extends AnyVal {
  type H[T] = F[A, T]
  def unaryKind: H[B] = value
}

//etc.

//Usage:
val result: ValidatedNel[Error, User] = (
  UserId(0).validNel.unaryKind,
  emailV.unaryKind,
  passV.unaryKind
).mapN(User)