feat: add Slice.SkipRef()

Author: justdmitry

TonLibDotNet/Cells/Slice.cs

@@ -218,5 +218,11 @@ public Cell PreloadRef()
             EnsureCanLoadRef();
             return refs![refIndex];
         }
+
+        public void SkipRef()
+        {
+            EnsureCanLoadRef();
+            refIndex++;
+        }
     }
 }