Refactor VM evaluation to use macro

The `eval` and `eval_observed` methods in the `VM` struct were very
similar, with the primary difference being the call to the `VMObserver`
trait. This commit refactors these methods into a single macro,
`dispatch_eval!`, which reduces code duplication and improves
maintainability.

The `Value::TailCallRequest` variant was also updated to use `Box` for
its contents, which helps keep the `Value` enum size consistent.

Finally, the benchmarks in the `examples` directory have been updated to
reflect minor performance changes resulting from these code
modifications.

src/ast/types.rs

@@ -70,7 +70,7 @@ pub enum Value {
     Function(Rc<dyn Fn(Vec<Value>) -> Value>),
     Object(Rc<dyn Object>), // For compiled Closures and other opaque types
     Cell(Rc<RefCell<Value>>), // Boxed value for captures
-    TailCallRequest(Rc<dyn Object>, Vec<Value>), // Internal: For TCO
+    TailCallRequest(Box<(Rc<dyn Object>, Vec<Value>)>), // Internal: For TCO (Boxed to keep Value small)
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
@@ -146,7 +146,7 @@ impl Value {
             Value::Function { .. } => StaticType::Any, // Dynamic function
             Value::Object(o) => StaticType::Object(o.type_name()),
             Value::Cell(c) => c.borrow().static_type(),
-            Value::TailCallRequest(_, _) => panic!("Internal VM state leaked: TailCallRequest"),
+            Value::TailCallRequest(_) => panic!("Internal VM state leaked: TailCallRequest"),
         }
     }
 }
@@ -181,7 +181,7 @@ impl fmt::Display for Value {
             Value::Function(_) => write!(f, "<native fn>"),
             Value::Object(o) => write!(f, "<{}>", o.type_name()),
             Value::Cell(c) => write!(f, "{}", c.borrow()),
-            Value::TailCallRequest(_, _) => panic!("Internal VM state leaked: TailCallRequest"),
+            Value::TailCallRequest(_) => panic!("Internal VM state leaked: TailCallRequest"),
         }
     }
 }