Import FreeCAD and Rhino files through cadmpeg (#1435)

FreeCAD .FCStd and Rhino .3dm files open, insert and drop like STEP and IGES:
cadmpeg (Apache-2.0, pinned =0.6.1, native builds only) detects the format,
decodes it under its service resource caps, validates the model and writes it
as STEP AP214, which becomes an Import feature in a new component named after
the file, with the up and names options.

Only the fcstd, rhino and step codecs are compiled in (no default features).
ACIS is left out: cadmpeg's sat codec is a ShapeManager stream decoder.
native_cad.rs is the single importer seam. Self-made FreeCAD and Rhino box
fixtures, hostile-input, ZIP-bomb and cap tests, engine tests for the
component path; the browser build reports these formats as not supported.
A note under design format 23 says an Import's file can name these formats.

Co-authored-by: Jacob Oursland <jacob.oursland@gmail.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/ui-egui/src/file_load.rs

@@ -125,11 +125,15 @@ const STAGED_THUMBNAIL_TRIANGLES: usize = 1_000_000;
 /// How long a frame spends on a staged STEP import.
 const STAGED_FRAME_MS: f64 = 30.0;
 
-/// Files read in stages: STEP (not IGES, which is first restated as STEP) to insert or open.
+/// Files read in stages: STEP (not IGES, FreeCAD or Rhino, which are first restated as STEP) to
+/// insert or open.
 #[cfg_attr(not(target_arch = "wasm32"), allow(dead_code))]
 fn staged_kind(request: &Request) -> bool {
     let p = &request.path;
-    matches!(request.kind, Kind::Insert | Kind::Open) && solidcraft_engine::io::is_step_path(p) && !solidcraft_engine::io::is_iges_path(p)
+    matches!(request.kind, Kind::Insert | Kind::Open)
+        && solidcraft_engine::io::is_step_path(p)
+        && !solidcraft_engine::io::is_iges_path(p)
+        && !solidcraft_engine::io::is_native_cad_path(p)
 }
 
 impl Running {