Refactor Value enum for Quote node

Replaces `Value::Object(Rc<dyn Object>)` for SyntaxNodes with a
dedicated `Value::Quote(Rc<SyntaxNode>)`. This provides better type
safety and clarity when dealing with AST nodes as values.
Refactor Value enum for Quote node

This commit introduces a new `Value::Quote` variant to represent quoted
AST nodes directly, replacing the generic `Value::Object` for this
purpose.

This change simplifies the handling of quoted nodes by:
- Directly storing an `Rc<SyntaxNode>` instead of relying on dynamic
  downcasting from `Rc<dyn Object>`.
- Streamlining macro expansion logic by removing the need to check for
  `SyntaxNode` within `Value::Object`.
- Improving type safety and explicitness in the `Value` enum.

src/ast/types.rs

@@ -1,4 +1,5 @@
 use crate::ast::closure::Closure;
+use crate::ast::nodes::SyntaxNode;
 use chrono::{TimeZone, Utc};
 use std::any::Any;
 use std::cell::RefCell;
@@ -263,7 +264,8 @@ pub enum Value {
     FieldAccessor(Keyword),
     Function(Rc<NativeFunction>),
     Closure(Rc<Closure>),     // Compiled function with captured upvalues
-    Object(Rc<dyn Object>),   // For Series, Streams, SyntaxNodes, and custom extensions
+    Quote(Rc<SyntaxNode>),    // Quoted AST node (from 'expr or macro expansion)
+    Object(Rc<dyn Object>),   // RTL extensions: Series, Streams, and custom types
     Cell(Rc<RefCell<Value>>), // Boxed value for captures
 }
 
@@ -284,6 +286,7 @@ impl PartialEq for Value {
             (Value::FieldAccessor(a), Value::FieldAccessor(b)) => a == b,
             (Value::Function(a), Value::Function(b)) => Rc::ptr_eq(a, b),
             (Value::Closure(a), Value::Closure(b)) => Rc::ptr_eq(a, b),
+            (Value::Quote(a), Value::Quote(b)) => Rc::ptr_eq(a, b),
             (Value::Object(a), Value::Object(b)) => Rc::ptr_eq(a, b),
             (Value::Cell(a), Value::Cell(b)) => Rc::ptr_eq(a, b),
             _ => false,
@@ -625,6 +628,7 @@ impl Value {
             Value::FieldAccessor(k) => StaticType::FieldAccessor(*k),
             Value::Function(_) => StaticType::Any, // Dynamic function
             Value::Closure(_) => StaticType::Object("closure"),
+            Value::Quote(_) => StaticType::Object("ast-node"),
             Value::Object(o) => StaticType::Object(o.type_name()),
             Value::Cell(c) => c.borrow().static_type(),
         }
@@ -669,6 +673,7 @@ impl fmt::Display for Value {
             Value::FieldAccessor(k) => write!(f, ".{}", k.name()),
             Value::Function(f_meta) => write!(f, "<native fn, {:?}>", f_meta.purity),
             Value::Closure(_) => write!(f, "<closure>"),
+            Value::Quote(_) => write!(f, "<ast-node>"),
             Value::Object(o) => write!(f, "<{:?}>", o),
             Value::Cell(c) => write!(f, "{}", c.borrow()),
         }