add a profiling test

tests/rlp/all_tests.nim

@@ -3,4 +3,5 @@ import
   ./test_json_suite,
   ./test_empty_string,
   ./test_object_serialization,
-  ./test_optional_fields
+  ./test_optional_fields,
+  ./test_rlp_profiler

tests/rlp/test_rlp_profiler.nim

@@ -0,0 +1,37 @@
+{.used.}
+
+import 
+  ../../eth/[rlp, common],
+  unittest2,
+  times,
+  os,
+  strutils
+
+template benchmark(benchmarkName: string, code: untyped) =
+  block:
+    let t0 = epochTime()
+    code
+    let elapsed = epochTime() - t0
+    let elapsedStr = elapsed.formatFloat(format = ffDecimal, precision = 9)
+    echo "CPU Time [", benchmarkName, "] ", elapsedStr, "s"
+
+const 
+  accesses  = @[AccessPair(
+    address: address"0x0000000000000000000000000000000000000001", 
+    storageKeys: @[default(Bytes32)]
+  )]
+
+let my_tx = Transaction(
+  txType:     TxEip1559,
+  chainId:    1.ChainId,
+  nonce:      0.AccountNonce,
+  gasLimit:   123457.GasInt,
+  maxPriorityFeePerGas: 42.GasInt,
+  maxFeePerGas: 10.GasInt,
+  accessList: accesses
+)
+
+suite "test running time of rlp serialization":
+  test "transaction serialization":
+    benchmark "Transaction":
+      let my_bytes = rlp.encode(my_tx)