Merge remote-tracking branch 'origin/main' into paultag/diff

- The `Node` type contained two enums by mistake. Those have been
   removed.

 - Export the `Visitor` and `Visitable` traits, as I start to migrate
   stuff to them.

 - Add a wrapper to pull the `digest` off the node without doing a
   `match` elsewhere.

src/wasm-lib/kcl/src/walk/mod.rs

@@ -3,4 +3,5 @@ mod ast_visitor;
 mod ast_walk;
 
 pub use ast_node::Node;
+pub use ast_visitor::{Visitable, Visitor};
 pub use ast_walk::walk;