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.

examples/macro_unless.myc

@@ -0,0 +1,8 @@
+;; Benchmark: 100ns
+;; Classic "unless" macro example
+;; Demonstrates simple template substitution.
+;; Output: 42
+
+(do
+    (macro unless [c b] `(if ~c void ~b))
+    (unless false 42))