Cargo: codec aad7053, kernel 1a52eaf, graph 263de59; honour viewport clipping

Brings codec PRs #84 (cross-version visual styles, table styles,
subentity managers), #88 (viewport clipping flag, DXF boundary handle),
#89 (DXF viewport snap/twist in degrees) and #92 (field format codes,
event updates).

With #88 a viewport keeps a stored boundary whether or not clipping is
on, so a linked boundary alone no longer means "clipped": rendering,
paper picking, VPCLIP and the Clipped property check the clipping flag
too, and VPCLIP / MVIEW Object and Polygon set it. Before, OCS never set
the flag, so its clipped viewports opened rectangular elsewhere.

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

src/scene/project.rs

@@ -507,7 +507,7 @@ impl Scene {
                 [xmin as f64, ymin as f64], [xmax as f64, ymin as f64],
                 [xmax as f64, ymax as f64], [xmin as f64, ymax as f64],
             ]];
-            if !self.images.is_empty() && !viewport.clip_boundary_handle.is_null() {
+            if !self.images.is_empty() && crate::entities::viewport::is_clipped(viewport) {
                 let boundary = self.clip_boundary_polygon(
                     viewport.clip_boundary_handle, viewport.center.z as f32);
                 if boundary.len() >= 3 {
@@ -663,7 +663,7 @@ impl Scene {
         if hw.abs() < 1e-6 || hh.abs() < 1e-6 {
             return vec![];
         }
-        let poly = if vp.clip_boundary_handle.is_null() {
+        let poly = if !crate::entities::viewport::is_clipped(vp) {
             // Rectangular viewport → its own four corners (paper coords). These
             // map to full-rect NDC [-1, 1], a no-op mask over a render target
             // that already clips to the rectangle, but it keeps rect and