[FS0670](https://github.com/pocketberserker/free-monad-fsharp/blob/bfbb9bab3e460aaad9ef2a009e70985c022492fb/FSharp.Monad.Free/CoYoneda.fs#L12) の問題を素晴らしい発想()で解決する案

CoYoneda.fs

namespace FSharp.Monad

type CoYoneda<'U> =
  abstract Run: obj -> 'U

type CoYoneda<'F, 'A>(fi: 'F, k: CoYoneda<'A>) = class end

module CoYoneda =
  
  let apply fa k =
    CoYoneda(fa, { new CoYoneda<_> with
      member this.Run(x) = box x |> k })