Add prelude and while macro

This commit introduces a new prelude file that defines the `while` macro
and registers it during environment bootstrapping. The `again` macro has
been updated to accept multiple arguments for its recursive call, and
several examples have been adjusted to reflect this change.
Additionally, the `MacroRegistry` in the compiler is now cloneable and
can be moved out of the `MacroExpander`.

src/ast/compiler/macros.rs

@@ -22,6 +22,7 @@ struct ExpansionState<'a> {
 type MacroMap = HashMap<Rc<str>, (Vec<Rc<str>>, Node<UntypedKind>)>;
 
 /// A registry for macro declarations.
+#[derive(Clone)]
 pub struct MacroRegistry {
     scopes: Vec<MacroMap>,
 }
@@ -78,6 +79,10 @@ impl<E: MacroEvaluator> MacroExpander<E> {
         }
     }
 
+    pub fn into_registry(self) -> MacroRegistry {
+        self.registry
+    }
+
     pub fn expand(&mut self, node: Node<UntypedKind>) -> Result<Node<UntypedKind>, String> {
         self.expand_recursive(node)
     }