Update function casting syntax after move to Scala 3

[michel-steuwer]

We should update the current function casting syntax

k.as[In `=` Array[Array[Float]] `,` Array[Float], Out[Array[Float]]]

towards

k.asFun[Args[Array[Array[Float]] `,` Array[Float]] => Array[Float]]

once we have moved to Scala 3. A sketch implementation is available here:
https://scastie.scala-lang.org/ndV4Xu8RQZWlZRYCc6GAig