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/vm.rs

@@ -258,6 +258,10 @@ macro_rules! dispatch_eval {
                     }
                 }
                 Ok(Value::Record(Rc::new(map)))
+            },
+
+            BoundKind::Expansion { original_call: _, bound_expanded } => {
+                $self.$eval_method($($observer,)? bound_expanded)
             }
         }
     };