Add debug mode and VM tracing

Introduce a `debug_mode` flag to the `Environment` and a new `run_debug`
method. This method uses a `TracingObserver` to log the VM's execution
flow, including node evaluation and scope state changes. This allows for
detailed inspection of script execution.

The `BoundKind` enum now also includes a `display_name` method for
better log readability.

src/ast/compiler/bound_nodes.rs

@@ -70,7 +70,24 @@ pub enum BoundKind {
     Map {
         entries: Vec<(Node<BoundKind, StaticType>, Node<BoundKind, StaticType>)>,
     },
-
-    // Extension points (need to be adapted for bound nodes if they use variables)
-    // For now, we assume extensions are self-contained or handled dynamically.
+}
+
+impl BoundKind {
+    pub fn display_name(&self) -> String {
+        match self {
+            BoundKind::Nop => "NOP".to_string(),
+            BoundKind::Constant(v) => format!("CONST({})", v),
+            BoundKind::Get(addr) => format!("GET({:?})", addr),
+            BoundKind::Set { addr, .. } => format!("SET({:?})", addr),
+            BoundKind::DefLocal { slot, .. } => format!("DEF_LOCAL(Slot:{})", slot),
+            BoundKind::If { .. } => "IF".to_string(),
+            BoundKind::DefGlobal { global_index, .. } => format!("DEF_GLOBAL(Idx:{})", global_index),
+            BoundKind::Lambda { upvalues, .. } => format!("LAMBDA(Captures:{})", upvalues.len()),
+            BoundKind::Call { .. } => "CALL".to_string(),
+            BoundKind::TailCall { .. } => "T-CALL".to_string(),
+            BoundKind::Block { .. } => "BLOCK".to_string(),
+            BoundKind::Tuple { elements } => format!("TUPLE({})", elements.len()),
+            BoundKind::Map { entries } => format!("MAP({})", entries.len()),
+        }
+    }
 }