Instance classes are recreated every time they're summoned

[neko-kai]

Because we're using implicit defs for type parameter polymorphism. We should cache the instances in lazy val and cast them, like some other libraries like monix do:

implicit def concurrentInstance[R]: Concurrent[RIO[R, *]] =
  concurrentInstance0.asInstanceOf[Concurrent[RIO[R, *]]

private[this] lazy val concurrentInstance0: Concurrent[RIO[Any, *]] = 
  new CatsConcurrent[Any]