fix 8119: Fix ReferenceError in snap object cache lookup

Cached SnapObj entries holding references to freed Blender
objects raised ReferenceError on .obj.name access. Evict
stale entries at the start of create_snap_obj.

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src/bonsai/bonsai/tool/raycast.py

@@ -888,6 +888,15 @@ class Raycast(bonsai.core.tool.Raycast):
     def create_snap_obj(cls, obj):
         if obj.data is None or not isinstance(obj.data, bpy.types.Mesh):
             return None
+        # Evict cached entries whose Blender object has since been freed.
+        valid = []
+        for s in cls.snap_objs:
+            try:
+                _ = s.obj.name
+                valid.append(s)
+            except ReferenceError:
+                pass
+        cls.snap_objs[:] = valid
         for i, snap_obj in enumerate(cls.snap_objs):
             if obj.name == snap_obj.obj.name:
                 # Handle objects modified while a modal operator is active.