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))