fix: uniformize domain stub

src/gen/gen.ml

@@ -53,7 +53,7 @@ type t = Thread.t
 
 let get_id (self:t) : int = Thread.id self
 
-let spawn_on f : t =
+let spawn f : t =
   Thread.create f ()
 |}
 

src/moonpool.ml

@@ -59,7 +59,7 @@ module D_pool_ = struct
       (let n = Domain_.recommended_number () in
        Array.init n (fun i ->
            let q = S_queue.create () in
-           let _domain : domain = Domain_.spawn_on (fun () -> work_ i q) in
+           let _domain : domain = Domain_.spawn (fun () -> work_ i q) in
            { q }))
 
   (** Number of domains in the pool *)