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 <[email protected]>
Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/solidcraft/src/main.rs

@@ -108,7 +108,7 @@ fn services(cc: &eframe::CreationContext<'_>) -> Services {
             let future = open_parent
                 .clone()
                 .add_filter(
-                    "Designs, STEP, IGES and meshes",
+                    "Designs, CAD files and meshes",
                     &[
                         io::DESIGN_EXT,
                         io::LEGACY_DESIGN_EXT,
@@ -121,6 +121,10 @@ fn services(cc: &eframe::CreationContext<'_>) -> Services {
                         "iges",
                         "IGS",
                         "IGES",
+                        "FCStd",
+                        "fcstd",
+                        "3dm",
+                        "3DM",
                         "3mf",
                         "3MF",
                         "stl",
@@ -136,6 +140,7 @@ fn services(cc: &eframe::CreationContext<'_>) -> Services {
                 .add_filter("SolidCraft design (container or JSON)", &[io::DESIGN_EXT, io::LEGACY_DESIGN_EXT, "json"])
                 .add_filter("STEP", &["step", "stp", "STEP", "STP"])
                 .add_filter("IGES", &["igs", "iges", "IGS", "IGES"])
+                .add_filter("FreeCAD and Rhino", &["FCStd", "fcstd", "3dm", "3DM"])
                 .add_filter("Mesh (3MF, STL, OBJ, glTF)", &["3mf", "3MF", "stl", "STL", "obj", "OBJ", "glb", "GLB", "gltf", "GLTF"])
                 .add_filter("Sketch drawings (DXF, SVG)", &["dxf", "DXF", "svg", "SVG"])
                 .add_filter("All files", &["*"])