core: refactor GASRecord handling

We should store each GAS record as
{
    Key: ContractID + RecordsPrefix + RecordID,
    Value: RecordValue,
}
So don't use state.GASRecord for storing anymore. However, it's still
useful to cache GasRecord values by using state.GASRecords, because we
have to keep GASIndexPairs sorted by indexes.

pkg/core/state/native_state_test.go

@@ -1,40 +0,0 @@
-package state
-
-import (
-	"math/big"
-	"testing"
-
-	"github.com/nspcc-dev/neo-go/pkg/internal/testserdes"
-	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
-	"github.com/stretchr/testify/require"
-)
-
-func TestGASRecord_EncodeBinary(t *testing.T) {
-	expected := &GASRecord{
-		GASIndexPair{
-			Index:       1,
-			GASPerBlock: *big.NewInt(123),
-		},
-		GASIndexPair{
-			Index:       2,
-			GASPerBlock: *big.NewInt(7),
-		},
-	}
-	testserdes.EncodeDecodeBinary(t, expected, new(GASRecord))
-}
-
-func TestGASRecord_fromStackItem(t *testing.T) {
-	t.Run("NotArray", func(t *testing.T) {
-		item := stackitem.Null{}
-		require.Error(t, new(GASRecord).fromStackItem(item))
-	})
-	t.Run("InvalidFormat", func(t *testing.T) {
-		item := stackitem.NewArray([]stackitem.Item{
-			stackitem.NewStruct([]stackitem.Item{
-				stackitem.NewBigInteger(big.NewInt(1)),
-				stackitem.NewBool(true),
-			}),
-		})
-		require.Error(t, new(GASRecord).fromStackItem(item))
-	})
-}