[Neo VM] optimize newstruct (#3525)

* optimize newstruct

* use Array.Fill

* Update src/Neo.VM/JumpTable/JumpTable.Compound.cs

---------

Co-authored-by: Shargon <shargon@gmail.com>

src/Neo.VM/JumpTable/JumpTable.Compound.cs

@@ -14,6 +14,7 @@
 using System.Linq;
 using System.Numerics;
 using System.Runtime.CompilerServices;
+using Array = System.Array;
 using VMArray = Neo.VM.Types.Array;
 
 namespace Neo.VM
@@ -151,8 +152,9 @@ public virtual void NewArray(ExecutionEngine engine, Instruction instruction)
             var n = (int)engine.Pop().GetInteger();
             if (n < 0 || n > engine.Limits.MaxStackSize)
                 throw new InvalidOperationException($"MaxStackSize exceed: {n}");
-
-            engine.Push(new VMArray(engine.ReferenceCounter, Enumerable.Repeat(StackItem.Null, n)));
+            var nullArray = new StackItem[n];
+            Array.Fill(nullArray, StackItem.Null);
+            engine.Push(new VMArray(engine.ReferenceCounter, nullArray));
         }
 
         /// <summary>
@@ -180,8 +182,9 @@ public virtual void NewArray_T(ExecutionEngine engine, Instruction instruction)
                 (byte)StackItemType.ByteString => ByteString.Empty,
                 _ => StackItem.Null
             };
-
-            engine.Push(new VMArray(engine.ReferenceCounter, Enumerable.Repeat(item, n)));
+            var itemArray = new StackItem[n];
+            Array.Fill(itemArray, item);
+            engine.Push(new VMArray(engine.ReferenceCounter, itemArray));
         }
 
         /// <summary>
@@ -210,10 +213,10 @@ public virtual void NewStruct(ExecutionEngine engine, Instruction instruction)
             var n = (int)engine.Pop().GetInteger();
             if (n < 0 || n > engine.Limits.MaxStackSize)
                 throw new InvalidOperationException($"MaxStackSize exceed: {n}");
-            Struct result = new(engine.ReferenceCounter);
-            for (var i = 0; i < n; i++)
-                result.Add(StackItem.Null);
-            engine.Push(result);
+
+            var nullArray = new StackItem[n];
+            Array.Fill(nullArray, StackItem.Null);
+            engine.Push(new Struct(engine.ReferenceCounter, nullArray));
         }
 
         /// <summary>