Make IndexedStateT contravariant on SA

Change from IndexedStateT[F[_], SA, SB, A] to IndexedStateT[F[_], -SA, SB, A]

Example of use:

trait Animal { def age: Int }
case class Cat(age: Int) extends Animal

val incrementCatAge: IndexedStateT[Id, Cat, Cat, Unit] = IndexedStateT.modify(cat => cat.copy(age = cat.age + 1))
val incrementAnimalAge: IndexedStateT[Id, Animal, Int, Unit] = IndexedStateT.modify(_.age + 1)

val composite = for {
  _ <- incrementCatAge
  _ <- incrementAnimalAge
  r <- IndexedStateT.get[Id, Int]
} yield r

Start at the IndexedStateT definition and inspect how its state type parameters are used. Typecheck the Animal and Cat composition example after making the requested variance change; done means the signature is contravariant on SA and the example compiles.