change %return syntax

cozo-core/src/cozoscript.pest

@@ -252,7 +252,7 @@ imperative_block = {imperative_stmt+}
 break_stmt = {"%break" ~ ident?}
 ignore_error_script = {"%ignore_error" ~ imperative_clause}
 continue_stmt = {"%continue" ~ ident?}
-return_stmt = {"%return" ~ (ident | underscore_ident | imperative_clause)*}
+return_stmt = {"%return" ~ (((ident | underscore_ident | imperative_clause) ~ ",")* ~ (ident | underscore_ident | imperative_clause))?}
 loop_block = {("%mark" ~ ident)? ~ "%loop" ~ imperative_block ~ "%end"}
 temp_swap = {"%swap" ~ underscore_ident ~ underscore_ident}
 debug_stmt = {"%debug" ~ (ident | underscore_ident)}