Add // line comments, grouped parentheses, and NODE_NOP

- Parse // comments in parse_statement by consuming tokens until newline
- Add NODE_NOP for no-op statements (comments)
- Support grouped expressions with parentheses in parse_term

projects/comment.j

@@ -0,0 +1,5 @@
+// Esto es un comentario
+println("Hello World!")
+
+// Otro comentario mas
+println(40)

projects/functions.j

@@ -1,2 +1,3 @@
 x = "Hello"
-println(len(x) + 3)
+y = 2 * (4 - 2)
+println(y)