Evict stale snap_objs cache entries on ReferenceError

When a Blender object is deleted while the snap cache still holds a
SnapObj referencing it, accessing snap_obj.obj.name raises ReferenceError.
Catch it, evict the dead entry, and let the caller retry cleanly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/bonsai/bonsai/tool/raycast.py

@@ -970,7 +970,12 @@ class Raycast(bonsai.core.tool.Raycast):
         if obj.data is None or not isinstance(obj.data, bpy.types.Mesh):
             return None
         for i, snap_obj in enumerate(cls.snap_objs):
-            if obj.name == snap_obj.obj.name:
+            try:
+                cached_name = snap_obj.obj.name
+            except ReferenceError:
+                cls.snap_objs.pop(i)
+                break
+            if obj.name == cached_name:
                 # Fast O(1) invalidation: vertex count change (mesh edit) or
                 # world matrix change (object moved/rotated).
                 if len(obj.data.vertices) != len(snap_obj.verts_3d):