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/lexer.rs

@@ -102,11 +102,12 @@ impl<'a> Lexer<'a> {
 
     fn skip_whitespace(&mut self) {
         while let Some(&c) = self.peek() {
-            if c.is_whitespace() {
+            if c.is_whitespace() || is_invisible(c) {
                 if c == '\n' {
                     self.line += 1;
                     self.col = 1;
-                } else {
+                } else if !is_invisible(c) {
+                    // Only increment column for characters that actually take space
                     self.col += 1;
                 }
                 self.input.next();
@@ -175,3 +176,17 @@ fn is_ident_start(c: char) -> bool {
 fn is_ident_char(c: char) -> bool {
     is_ident_start(c) || c.is_ascii_digit()
 }
+
+/// Returns true if the character is an invisible control character 
+/// that should be ignored by the lexer (like BOM or Zero Width Space).
+fn is_invisible(c: char) -> bool {
+    match c {
+        '\u{FEFF}' | // BOM
+        '\u{200B}' | // Zero Width Space
+        '\u{200C}' | // Zero Width Non-Joiner
+        '\u{200D}' | // Zero Width Joiner
+        '\u{2060}'   // Word Joiner
+        => true,
+        _ => false,
+    }
+}