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/types.rs

@@ -91,6 +91,38 @@ pub enum StaticType {
     Object(&'static str),
 }
 
+impl fmt::Display for StaticType {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            StaticType::Any => write!(f, "any"),
+            StaticType::Void => write!(f, "void"),
+            StaticType::Bool => write!(f, "bool"),
+            StaticType::Int => write!(f, "int"),
+            StaticType::Float => write!(f, "float"),
+            StaticType::Text => write!(f, "text"),
+            StaticType::Keyword => write!(f, "keyword"),
+            StaticType::List(inner) => write!(f, "[{}]", inner),
+            StaticType::Record(fields) => {
+                write!(f, "{{")?;
+                for (i, (k, v)) in fields.iter().enumerate() {
+                    if i > 0 { write!(f, ", ")?; }
+                    write!(f, ":{} {}", k.name(), v)?;
+                }
+                write!(f, "}}")
+            },
+            StaticType::Function { params, ret } => {
+                write!(f, "fn(")?;
+                for (i, p) in params.iter().enumerate() {
+                    if i > 0 { write!(f, " ")?; }
+                    write!(f, "{}", p)?;
+                }
+                write!(f, ") -> {}", ret)
+            },
+            StaticType::Object(name) => write!(f, "{}", name),
+        }
+    }
+}
+
 impl Value {
     pub fn is_truthy(&self) -> bool {
         match self {