client: add GetOraclePrice for oracle price

pkg/rpc/client/native.go

@@ -0,0 +1,18 @@
+package client
+
+// Various non-policy things from native contracs.
+
+import (
+	"fmt"
+
+	"github.com/nspcc-dev/neo-go/pkg/core/native/nativenames"
+)
+
+// GetOraclePrice invokes `getPrice` method on a native Oracle contract.
+func (c *Client) GetOraclePrice() (int64, error) {
+	oracleHash, err := c.GetNativeContractHash(nativenames.Notary)
+	if err != nil {
+		return 0, fmt.Errorf("failed to get native Oracle hash: %w", err)
+	}
+	return c.invokeNativeGetMethod(oracleHash, "getPrice")
+}