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/compiler/upvalues.rs

@@ -93,6 +93,12 @@ impl UpvalueAnalyzer {
                     Self::visit(v, scopes, capture_map, current_lambda.clone());
                 }
             }
+            UntypedKind::Expansion { call: _, expanded } => {
+                Self::visit(expanded, scopes, capture_map, current_lambda);
+            }
+            UntypedKind::MacroDecl { body, .. } | UntypedKind::Template(body) | UntypedKind::Placeholder(body) | UntypedKind::Splice(body) => {
+                Self::visit(body, scopes, capture_map, current_lambda);
+            }
             UntypedKind::Nop | UntypedKind::Constant(_) | UntypedKind::Extension(_) => {}
         }
     }