Simplify app development with dedicated API for tasks not depending on volatile process state

[Viir]

So far, we always use volatile processes to run tasks integrating other software. However, in many cases, we don't need the facilities to retain volatile process state beyond a single task. Examples are usages of elm-format and elm make in Elm Editor.

A dedicated API for a single task would simplify application developers' implementation. For example, this part should be simpler (And more complete, forwarding any errors that were not linked to RequestToVolatileProcess): https://github.com/pine-vm/pine/blob/e4949e0d1fdfe7eba8dd326f8429b8765276dc6e/implement/example-apps/elm-editor/src/Backend/Main.elm#L370-L377