Show a bounded native-cache preview before authoritative reconstruction (#463)

Refs #303. file.save / file.save_as can store a warm native geometry cache (cache: true, off by default) keyed to the document hash, app version and adapter revision. Opening shows a bounded preview from it until the rebuilt session replaces it. Any cache failure counts as a miss.

crates/kernel/src/lib.rs

@@ -85,7 +85,7 @@ pub use lip::raise_band;
 pub use measure::{BodyMeasure, measure};
 pub use mesh_convert::convert_prismatic_mesh;
 pub use meshbody::{MAX_TRIANGLES, mesh_body};
-pub use native::{decode_native_body, encode_native_body};
+pub use native::{decode_native_body, encode_native_body, native_preview_mesh};
 pub use offset::with_same_surface;
 pub use ops::{BoolOp, boolean, can_join_touching_faces, split_by_plane, transform, transform_matrix, union_apart};
 pub use polybool::{faceted_boolean, planar_boolean};