core: add cachedDao to cache accounts and contracts

Importing 100K blocks starting at 1.4M, before this patch:
real    6m0,356s
user    8m52,293s
sys     0m47,372s

After this patch:
real    4m17,748s
user    6m23,316s
sys     0m37,866s

Almost 30% better.

pkg/core/cacheddao_test.go

@@ -0,0 +1,83 @@
+package core
+
+import (
+	"testing"
+
+	"github.com/CityOfZion/neo-go/pkg/core/state"
+	"github.com/CityOfZion/neo-go/pkg/core/storage"
+	"github.com/CityOfZion/neo-go/pkg/crypto/hash"
+	"github.com/CityOfZion/neo-go/pkg/internal/random"
+	"github.com/CityOfZion/neo-go/pkg/smartcontract"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCachedDaoAccounts(t *testing.T) {
+	store := storage.NewMemoryStore()
+	// Persistent DAO to check for backing storage.
+	pdao := newDao(store)
+	// Cached DAO.
+	cdao := newCachedDao(store)
+
+	hash := random.Uint160()
+	_, err := cdao.GetAccountState(hash)
+	require.NotNil(t, err)
+
+	acc, err := cdao.GetAccountStateOrNew(hash)
+	require.Nil(t, err)
+	_, err = pdao.GetAccountState(hash)
+	require.NotNil(t, err)
+
+	acc.Version = 42
+	require.NoError(t, cdao.PutAccountState(acc))
+	_, err = pdao.GetAccountState(hash)
+	require.NotNil(t, err)
+
+	acc2, err := cdao.GetAccountState(hash)
+	require.Nil(t, err)
+	require.Equal(t, acc, acc2)
+
+	acc2, err = cdao.GetAccountStateOrNew(hash)
+	require.Nil(t, err)
+	require.Equal(t, acc, acc2)
+
+	_, err = cdao.Persist()
+	require.Nil(t, err)
+
+	acct, err := pdao.GetAccountState(hash)
+	require.Nil(t, err)
+	require.Equal(t, acc, acct)
+}
+
+func TestCachedDaoContracts(t *testing.T) {
+	store := storage.NewMemoryStore()
+	dao := newCachedDao(store)
+
+	script := []byte{0xde, 0xad, 0xbe, 0xef}
+	sh := hash.Hash160(script)
+	_, err := dao.GetContractState(sh)
+	require.NotNil(t, err)
+
+	cs := &state.Contract{}
+	cs.Name = "test"
+	cs.Script = script
+	cs.ParamList = []smartcontract.ParamType{1, 2}
+
+	require.NoError(t, dao.PutContractState(cs))
+	cs2, err := dao.GetContractState(sh)
+	require.Nil(t, err)
+	require.Equal(t, cs, cs2)
+
+	_, err = dao.Persist()
+	require.Nil(t, err)
+	dao2 := newCachedDao(store)
+	cs2, err = dao2.GetContractState(sh)
+	require.Nil(t, err)
+	require.Equal(t, cs, cs2)
+
+	require.NoError(t, dao.DeleteContractState(sh))
+	cs2, err = dao2.GetContractState(sh)
+	require.Nil(t, err)
+	require.Equal(t, cs, cs2)
+	_, err = dao.GetContractState(sh)
+	require.NotNil(t, err)
+}