Remove redundant allocation in Rlp.Encode<T> when input is already Rlp

src/Nethermind/Nethermind.Serialization.Rlp/Rlp.cs

@@ -328,8 +328,7 @@ public static Rlp Encode<T>(T item, RlpBehaviors behaviors = RlpBehaviors.None)
         {
             if (item is Rlp rlp)
             {
-                RlpStream stream = new(LengthOfSequence(rlp.Length));
-                return new(stream.Data.ToArray());
+                return rlp;
             }
 
             IRlpStreamDecoder<T>? rlpStreamDecoder = GetStreamDecoder<T>();