feat: Implement AST macros and templates

This commit introduces support for AST macros and templates, enabling
users to define and use custom, reusable components within the visual
DSL.

Key changes include:
- A new `MacroRegistry` to manage macro definitions.
- A `MacroExpander` to process macro calls and expand templates.
- A `MacroEvaluator` trait for evaluating expressions during expansion.
- The `Expansion` node in `BoundKind` to preserve the original macro
  call and its expanded form for debugging.
- Updates to the `Binder`, `Dumper`, and `UpvalueAnalyzer` to handle the
  new macro constructs.
- New examples demonstrating various macro functionalities like
  `unless`, splicing, and nested macros.

src/ast/nodes.rs

@@ -1,6 +1,7 @@
 use std::rc::Rc;
 use std::fmt::Debug;
-use crate::ast::types::{Identity, Value};
+use std::any::Any;
+use crate::ast::types::{Identity, Value, Object};
 
 /// A generic AST Node wrapper to preserve identity and metadata
 #[derive(Debug, Clone)]
@@ -10,12 +11,28 @@ pub struct Node<K, T = ()> {
     pub ty: T,
 }
 
+impl Object for Node<UntypedKind> {
+    fn type_name(&self) -> &'static str {
+        "ast-node"
+    }
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+}
+
 /// The base for custom node types (extensions)
 pub trait CustomNode: Debug {
     fn display_name(&self) -> &'static str;
+    fn clone_box(&self) -> Box<dyn CustomNode>;
 }
 
-#[derive(Debug)]
+impl Clone for Box<dyn CustomNode> {
+    fn clone(&self) -> Self {
+        self.clone_box()
+    }
+}
+
+#[derive(Debug, Clone)]
 pub enum UntypedKind {
     Nop,
     Constant(Value),
@@ -50,5 +67,24 @@ pub enum UntypedKind {
     Map {
         entries: Vec<(Node<UntypedKind>, Node<UntypedKind>)>,
     },
+    /// A macro declaration that can be expanded at compile time.
+    MacroDecl {
+        name: Rc<str>,
+        params: Vec<Rc<str>>,
+        body: Box<Node<UntypedKind>>,
+    },
+    /// A template for AST nodes, allowing for substitutions. (Quasiquote)
+    Template(Box<Node<UntypedKind>>),
+    /// A placeholder inside a template to be replaced by a node or value. (Unquote)
+    Placeholder(Box<Node<UntypedKind>>),
+    /// A placeholder that flattens a sequence or merges a map into its surroundings. (Splice)
+    Splice(Box<Node<UntypedKind>>),
+    /// Represents an expanded macro call, preserving the original call for debugging.
+    Expansion {
+        /// The original call from the source AST.
+        call: Box<Node<UntypedKind>>,
+        /// The resulting AST after macro expansion.
+        expanded: Box<Node<UntypedKind>>,
+    },
     Extension(Box<dyn CustomNode>),
 }