feat: add ToGrid() method to extended grid

src/Grid.fs

@@ -548,6 +548,14 @@ type ExtendedGrid(grid: IGrid) =
 
     member this.Grid = grid
 
+    member this.ToGrid() =
+        {
+            Nodes = this.Grid.getVertices ()
+            Elem = this.Grid.getCells ()
+            BBox = this.Grid.getBoundingBox ()
+        }
+
+
     member this.initNeighborIndex(?cache: string) =
         match neighborIndex with
         | Some _ -> ()