vm: support uint8 and uint64 in makeStackItem()

Convenience to avoid casts, uint64 is also a bit special in that it can't be
converted to int64 without data loss.

pkg/vm/stack_item.go

@@ -1,6 +1,7 @@
 package vm
 
 import (
+	"encoding/binary"
 	"encoding/json"
 	"fmt"
 	"math/big"
@@ -23,6 +24,10 @@ func makeStackItem(v interface{}) StackItem {
 		return &BigIntegerItem{
 			value: big.NewInt(val),
 		}
+	case uint8:
+		return &BigIntegerItem{
+			value: big.NewInt(int64(val)),
+		}
 	case uint16:
 		return &BigIntegerItem{
 			value: big.NewInt(int64(val)),
@@ -31,6 +36,14 @@ func makeStackItem(v interface{}) StackItem {
 		return &BigIntegerItem{
 			value: big.NewInt(int64(val)),
 		}
+	case uint64:
+		b := make([]byte, 8)
+		binary.BigEndian.PutUint64(b, val)
+		bigInt := big.NewInt(0)
+		bigInt.SetBytes(b)
+		return &BigIntegerItem{
+			value: bigInt,
+		}
 	case []byte:
 		return &ByteArrayItem{
 			value: val,