codegen: implement "without rowid" tables

ops/gas_init_test.sh

@@ -46,11 +46,19 @@ create table items (
     created_at integer not null,
     updated_at integer not null
 ) strict;
+
+create table item_to_item (
+    item1_id integer references items(rowid),
+    item2_id integer references items(rowid),
+    primary key (item1_id, item2_id)
+) strict, without rowid;
+
 EOF
 
 # Generate an item model and test file
 $gas generate items > pkg/db/item.go
 $gas generate items --test > pkg/db/item_test.go
+$gas generate item_to_item > pkg/db/item_to_item.go
 go mod tidy
 
 # Run the tests