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>

Cargo.toml

@@ -57,6 +57,14 @@ quick-xml = "0.41"
 # read by crates/io itself, so no image decoding or file access comes with it.
 gltf = { version = "1.4", default-features = false, features = ["names"] }
 
+# FreeCAD and Rhino import (Apache-2.0, pure Rust apart from zstd; native builds only).
+# Pinned: its IR and codec APIs change between minor versions. Open formats only: no default
+# features, so cadmpeg's codecs for commercial formats (f3d, sldprt, inventor, catia, creo, nx)
+# and its ShapeManager/ACIS `sat` codec are not compiled in. `step` is the writer we restate through.
+cadmpeg-core = "=0.6.1"
+cadmpeg-ir = "=0.6.1"
+cadmpeg-registry = { version = "=0.6.1", default-features = false, features = ["fcstd", "rhino", "step"] }
+
 # fonts (sketch text outlines; MIT OR Apache-2.0, pure Rust)
 ttf-parser = { version = "0.25", default-features = false, features = ["std"] }