test: use State.t instead of 'st intest/skeleton/ to ease the life of Ocaml beginners

test/skeleton/p.ml

-(* Time-stamp: <modified the 16/01/2023 (at 21:58) by Erwan Jahier> *)
+(* Time-stamp: <modified the 29/06/2023 (at 16:04) by Erwan Jahier> *)
 
 (* a dumb algo that compiles *)
 
 open Algo
 
-let (init_state: int -> string -> 'st) =
+let (init_state: int -> string -> State.t) =
   fun _nl _ -> (Random.int 10)
 
 
-let (enable_f: 'st -> 'st neighbor list -> action list) =
+let (enable_f: State.t -> State.t neighbor list -> action list) =
   fun _ nl ->
     match state (List.hd nl) with
     | 0 ->  ["action2"]
@@ -16,7 +16,7 @@ let (enable_f: 'st -> 'st neighbor list -> action list) =
     | _ ->  ["action1"]
 
 
-let (step_f : 'st -> 'st neighbor list -> action -> 'st ) =
+let (step_f : State.t -> State.t neighbor list -> action -> State.t ) =
   fun e _ ->
     function
     | "action1" -> 0