lang: replace stack-based parser with a recursive parser

lang/parse/label.c

@@ -0,0 +1,18 @@
+#include "ctx.h"
+
+bool peek_label(struct ivy_parser *parser)
+{
+	struct ivy_token *tok = peek_token(parser);
+	return (!tok || tok->t_type == IVY_TOK_LABEL);
+}
+
+bool parse_label(struct ivy_parser *parser, struct ivy_token **out)
+{
+	struct ivy_token *tok = peek_token(parser);
+	if (!tok || tok->t_type != IVY_TOK_LABEL) {
+		return false;
+	}
+
+	*out = parse_token(parser);
+	return true;
+}