Small optimizations using cached VM Script

src/neo/Ledger/Blockchain.cs

@@ -53,7 +53,7 @@ public class FillCompleted { }
             Transactions = new[] { DeployNativeContracts() }
         };
 
-        private readonly static byte[] onPersistNativeContractScript;
+        private readonly static Script onPersistNativeContractScript;
         private const int MaxTxToReverifyPerIdle = 10;
         private static readonly object lockObj = new object();
         private readonly NeoSystem system;
@@ -323,8 +323,7 @@ private RelayResultReason OnNewBlock(Block block)
                     using (Snapshot snapshot = GetSnapshot())
                     {
                         snapshot.Blocks.Add(block.Hash, block.Header.Trim());
-                        snapshot.HeaderHashIndex.GetAndChange().Hash = block.Hash;
-                        snapshot.HeaderHashIndex.GetAndChange().Index = block.Index;
+                        snapshot.HeaderHashIndex.GetAndChange().Set(block);
                         SaveHeaderHashList(snapshot);
                         snapshot.Commit();
                     }

src/neo/Network/P2P/Payloads/Header.cs

@@ -1,9 +1,7 @@
 using Neo.IO.Json;
 using Neo.Ledger;
-using Neo.Wallets;
 using System;
 using System.IO;
-using System.Linq;
 
 namespace Neo.Network.P2P.Payloads
 {

src/neo/SmartContract/Helper.cs

@@ -284,8 +284,8 @@ internal static bool VerifyWitnesses(this IVerifiable verifiable, Snapshot snaps
                 {
                     engine.LoadScript(verification);
                     engine.LoadScript(verifiable.Witnesses[i].InvocationScript);
-                    if (engine.Execute().HasFlag(VMState.FAULT)) return false;
-                    if (engine.ResultStack.Count != 1 || !engine.ResultStack.Pop().ToBoolean()) return false;
+                    if (engine.Execute() == VMState.FAULT) return false;
+                    if (!engine.ResultStack.TryPop(out var result) || !result.ToBoolean()) return false;
                 }
             }
             return true;