rpc: improve RPC Client initialization

Thanks to #2463.

pkg/rpc/client/client.go

@@ -13,7 +13,6 @@ import (
 	"time"
 
 	"github.com/nspcc-dev/neo-go/pkg/config/netmode"
-	"github.com/nspcc-dev/neo-go/pkg/core/native/nativenames"
 	"github.com/nspcc-dev/neo-go/pkg/rpc/request"
 	"github.com/nspcc-dev/neo-go/pkg/rpc/response"
 	"github.com/nspcc-dev/neo-go/pkg/util"
@@ -146,6 +145,10 @@ func (c *Client) Init() error {
 	if err != nil {
 		return fmt.Errorf("failed to get network magic: %w", err)
 	}
+	natives, err := c.GetNativeContracts()
+	if err != nil {
+		return fmt.Errorf("failed to get native contracts: %w", err)
+	}
 
 	c.cacheLock.Lock()
 	defer c.cacheLock.Unlock()
@@ -156,21 +159,10 @@ func (c *Client) Init() error {
 		c.cache.network = version.Magic
 		c.cache.stateRootInHeader = version.StateRootInHeader
 	}
-	neoContractHash, err := c.GetContractStateByAddressOrName(nativenames.Neo)
-	if err != nil {
-		return fmt.Errorf("failed to get NEO contract scripthash: %w", err)
+	for _, ctr := range natives {
+		c.cache.nativeHashes[ctr.Manifest.Name] = ctr.Hash
 	}
-	c.cache.nativeHashes[nativenames.Neo] = neoContractHash.Hash
-	gasContractHash, err := c.GetContractStateByAddressOrName(nativenames.Gas)
-	if err != nil {
-		return fmt.Errorf("failed to get GAS contract scripthash: %w", err)
-	}
-	c.cache.nativeHashes[nativenames.Gas] = gasContractHash.Hash
-	policyContractHash, err := c.GetContractStateByAddressOrName(nativenames.Policy)
-	if err != nil {
-		return fmt.Errorf("failed to get Policy contract scripthash: %w", err)
-	}
-	c.cache.nativeHashes[nativenames.Policy] = policyContractHash.Hash
+
 	c.cache.initDone = true
 	return nil
 }