IMPORT: read SAT, STEP, IGES and WMF files; ACISIN and WMFIN

ACIS text files come in one object per body (3DSOLID, REGION or SURFACE).
STEP B-rep models become a block per product with component inserts at
their placements, scaled to the drawing's units; IGES manifold solids come
in as 3DSOLIDs scaled to the drawing's units with their colours. Splines
that are exactly analytic shapes are kept as those shapes. Windows
metafiles become a WMF<n> block of polylines and text fitted to half the
view, placed at its top-left corner or by WMFIN's insertion prompts. The
Import File window lists the four formats as supported.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/commands/mod.rs

@@ -20,6 +20,7 @@ mod fileops;
 mod inquiry;
 mod layerprops;
 mod layers;
+mod model_import;
 mod pc_colormap;
 mod pc_extract;
 mod pdf_dialogs;
@@ -393,6 +394,9 @@ impl OpenCADStudio {
         if let Some(t) = self.dispatch_import(cmd, i) {
             return Some(t);
         }
+        if let Some(t) = self.dispatch_model_import(cmd, i) {
+            return Some(t);
+        }
         if let Some(t) = self.dispatch_bvisibility(cmd, i) {
             return Some(t);
         }
@@ -994,6 +998,8 @@ inventory::submit!(crate::command::CommandRegistration {
         "QNEW",
         "OBJIMPORT",
         "IMPORT",
+        "ACISIN",
+        "WMFIN",
         "DGNIMPORT",
         "-DGNIMPORT",
         "OPEN",