Make minor adjustments to browse example (#98)

## Description

This adds a total node count to the `async_browse` example and uses
human-readable output for [node
classes](https://reference.opcfoundation.org/Core/Part3/v104/docs/8.30#_Ref130971442)
instead of the underlying node class index.

Co-authored-by: Uwe Klotz <uwe.klotz@gmail.com>

examples/async_browse.rs

@@ -20,11 +20,13 @@ async fn main() -> anyhow::Result<()> {
             return format!("{node_id}");
         };
 
-        let info = format!("{}, {:?}", node.display_name().text(), node.node_class());
+        let info = format!("{}, {}", node.display_name().text(), node.node_class());
 
         format!("{name} ({info}) -> {node_id}")
     });
 
+    println!("{} nodes in total", hierarchy.node_count());
+
     Ok(())
 }
 
@@ -214,6 +216,10 @@ impl<T> TreeNode<T> {
         root_node
     }
 
+    fn node_count(&self) -> usize {
+        1 + self.children.values().map(Self::node_count).sum::<usize>()
+    }
+
     fn pretty_print<FL>(&self, mut label: FL)
     where
         FL: FnMut(Option<&str>, &T) -> String,