Compile-time refinement for cons

It would be cool if this worked:

```scala
type NonEmptySeq[A] = immutable.Seq[A] Refined NonEmpty

object NonEmptySeq {
def apply[A]: RefinedTypeOps[NonEmptySeq[A], immutable.Seq[A]] = {
new RefinedTypeOps[NonEmptySeq[A], immutable.Seq[A]]
}
}

val a = "refined"
val b = "types" :: "are" :: "cool!"
NonEmptySeq[String](a :: b)
// or at least
NonEmptySeq[String](::(a, b))
```

Start by tracing RefinedTypeOps and the NonEmpty refinement used in the example. Done means determining whether the shown NonEmptySeq calls, including the alternative :: form, can compile-time refine a non-empty sequence and documenting or implementing the supported scope.

Written by the indexing model from the issue text.