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/doc/src/lib.rs

@@ -40,6 +40,7 @@ pub use profile_refs::{capture_profile_selection, profile_selection_indices};
 pub mod plastic;
 pub mod project;
 mod project3d;
+pub mod render_settings;
 pub use project3d::iso_grid;
 pub mod sheet;