feat: update ContractExecutor and implementation classes

use default function of interface to update ContractExecutor; add TODO logs in SelfAdaptiveShardingExecutor

src/main/java/org/bdware/server/trustedmodel/ContractExecutor.java

@@ -5,4 +5,7 @@ import org.bdware.sc.conn.ResultCallback;
 
 public interface ContractExecutor {
     void execute(String requestID, ResultCallback rc, ContractRequest req);
+
+    default void close() {
+    }
 }