Fix: Use NOP instead of void in unless macro

The `unless` macro's expansion was updated to use `...` (NOP) instead of
`void`. This change also involved removing the `void` keyword from the
parser, as it is no longer used.

examples/macro_unless.myc

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

src/ast/compiler/macros.rs

@@ -481,7 +481,7 @@ mod tests {
     fn test_macro_expansion_unless() {
         let source = "
             (do
-                (macro unless [c b] `(if ~c void ~b))
+                (macro unless [c b] `(if ~c ... ~b))
                 (unless false 42))
         ";
         let mut parser = Parser::new(source).unwrap();
@@ -496,7 +496,7 @@ mod tests {
                     if let UntypedKind::Identifier(sym) = &cond.kind {
                         assert_eq!(sym.name.as_ref(), "false");
                     } else { panic!("Expected identifier 'false', got {:?}", cond.kind); }
-                    assert!(matches!(then_br.kind, UntypedKind::Constant(Value::Void)));
+                    assert!(matches!(then_br.kind, UntypedKind::Nop));
                     if let Some(eb) = else_br {
                         if let UntypedKind::Constant(Value::Int(n)) = &eb.kind {
                             assert_eq!(*n, 42);

src/ast/parser.rs

@@ -92,7 +92,6 @@ impl<'a> Parser<'a> {
             TokenKind::Identifier(id) => {
                 match id.as_ref() {
                     "..." => UntypedKind::Nop,
-                    "void" => UntypedKind::Constant(Value::Void),
                     _ => UntypedKind::Identifier(id.into()),
                 }
             }