feat: save body and occurrence visibility with the design (#531) (#592)

Hidden bodies, occurrence placements, sketches and origin items are saved with the design and come back when it is reopened. Visibility is still not an undo step, but hiding or showing something now counts as an unsaved change. Additive field under format 16. Fixes #531.

Co-authored-by: jonaswre <jonas.wrede@beyondit.gmbh>

crates/mcp/src/tests.rs

@@ -483,7 +483,6 @@ fn compact_batch_reply_does_not_repeat_the_body_list() {
 /// #531: a product model keeps an optional variant hidden in its default presentation. Hiding
 /// it must survive saving and reopening the design (suppressing it would change the design).
 #[test]
-#[ignore = "fails until #531 is fixed"]
 fn hidden_body_stays_hidden_after_save_and_reopen() {
     let mut s = server();
     tool(&mut s, "execute", json!({"command": "solid.box", "params": {"length": 10, "width": 10, "height": 10, "body_name": "Base"}}));