Render R2: persist named render setups without re-evaluating geometry (#667)

render.settings.set saves validated named render setups (camera, output size, exposure, environment) as one undo step, and render.settings.get reads them back without applying a camera. When validated render settings are the only change, the engine keeps the evaluated model instead of rebuilding it. Setups are saved under design format 21; format-20 designs read as having none. Fixes #658; refs #620.

Contributed by @0xlillith.

Co-authored-by: lillith <35337584+0xlillith@users.noreply.github.com>

crates/io/src/design.rs

@@ -1128,7 +1128,10 @@ mod tests {
         doc.units = "in".into();
         doc.named_views.push(solidcraft_doc::NamedView { name: "View".into(), ..Default::default() });
         doc.param_comments.insert("test".into(), "metadata".into());
+        let setup = solidcraft_doc::render_settings::RenderSetup { exposure_ev: 1.5, ..Default::default() };
+        std::sync::Arc::make_mut(&mut doc.render).setups.insert("Studio".into(), setup);
         let expected = crate::read_design(&crate::write_design(&doc)).unwrap();
+        assert_eq!(expected.render, doc.render);
         assert_eq!(crate::read_design(&write_design_container(&doc).unwrap()).unwrap(), expected);
     }