AppendCpsTree
append cps tree, which is frs and then snd. we use this representation instead Mapped/Flatmapped in cases, where we later can apply await to append term and simplify tree instead wrapping awaited tree in extra flatMap
append cps tree, which is frs and then snd. we use this representation instead Mapped/Flatmapped in cases, where we later can apply await to append term and simplify tree instead wrapping awaited tree in extra flatMap