fix(engine): impl_infos can be duplicated because of names crate

Author: W95Psp

engine/lib/concrete_ident/concrete_ident.ml

@@ -174,7 +174,8 @@ end = struct
     state :=
       impl_infos
       |> List.map ~f:(map_fst Imported.of_def_id)
-      |> Hashtbl.of_alist_exn (module T)
+      |> Hashtbl.of_alist_multi (module T)
+      |> Hashtbl.map ~f:List.hd_exn
       |> Option.some
 
   let get_state () =