lang: replace stack-based parser with a recursive parser

lang/ast/return.c

@@ -1,4 +1,3 @@
-#include "ctx.h"
 #include "iterate.h"
 #include "node.h"
 
@@ -14,6 +13,5 @@ static void collect_children(
 
 struct ast_node_type return_node_ops = {
 	.n_collect_children = collect_children,
-	.n_state_size = sizeof(struct parser_state),
 	.n_node_size = sizeof(struct ivy_ast_return_node),
 };