fix(physics): validate retail cell containment roots

tests/AcDream.App.Tests/Streaming/LandblockPhysicsPublisherTests.cs

@@ -879,6 +879,13 @@ public sealed class LandblockPhysicsPublisherTests
             {
                 [0] = new Polygon { VertexIds = [0, 1, 2] },
             },
+            CellBSP = new CellBSPTree
+            {
+                Root = new CellBSPNode
+                {
+                    Type = DatReaderWriter.Enums.BSPNodeType.Leaf,
+                },
+            },
         };
         var environment = new DatReaderWriter.DBObjs.Environment
         {