node/visitor: add module skeleton

src/node/mod.rs

@@ -12,3 +12,4 @@ use crate::event::types::Slice;
 pub(crate) mod error;
 mod graph;
 mod nodes;
+mod visitor;

src/node/visitor/mod.rs

@@ -0,0 +1,5 @@
+/*
+ * This Source Code Form is subject to the terms of the
+ * Mozilla Public License, v. 2.0. If a copy of the MPL
+ * was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */