chore(dslocal): refine few typespecs

apps/emqx_ds_builtin_local/src/emqx_ds_builtin_local.erl

@@ -304,7 +304,7 @@ get_streams(DB, TopicFilter, StartTime) ->
 -spec make_iterator(
     emqx_ds:db(), emqx_ds:ds_specific_stream(), emqx_ds:topic_filter(), emqx_ds:time()
 ) ->
-    emqx_ds:make_iterator_result(emqx_ds:ds_specific_iterator()).
+    emqx_ds:make_iterator_result(iterator()).
 make_iterator(DB, ?stream(Shard, InnerStream), TopicFilter, StartTime) ->
     ShardId = {DB, Shard},
     case
@@ -318,7 +318,7 @@ make_iterator(DB, ?stream(Shard, InnerStream), TopicFilter, StartTime) ->
             Error
     end.
 
--spec update_iterator(emqx_ds:db(), emqx_ds:ds_specific_iterator(), emqx_ds:message_key()) ->
+-spec update_iterator(emqx_ds:db(), iterator(), emqx_ds:message_key()) ->
     emqx_ds:make_iterator_result(iterator()).
 update_iterator(DB, Iter0 = #{?tag := ?IT, ?shard := Shard, ?enc := StorageIter0}, Key) ->
     case emqx_ds_storage_layer:update_iterator({DB, Shard}, StorageIter0, Key) of
@@ -396,7 +396,7 @@ do_next(DB, Iter0 = #{?tag := ?IT, ?shard := Shard, ?enc := StorageIter0}, N) ->
     end.
 
 -spec do_delete_next(emqx_ds:db(), delete_iterator(), emqx_ds:delete_selector(), pos_integer()) ->
-    emqx_ds:delete_next_result(emqx_ds:delete_iterator()).
+    emqx_ds:delete_next_result(delete_iterator()).
 do_delete_next(
     DB, Iter = #{?tag := ?DELETE_IT, ?shard := Shard, ?enc := StorageIter0}, Selector, N
 ) ->