Fix memory leak

Author: ennuite

flight/flight-sql-jdbc-core/src/main/java/org/apache/arrow/driver/jdbc/ArrowFlightConnection.java

@@ -20,6 +20,7 @@
 
 import io.netty.util.concurrent.DefaultThreadFactory;
 import java.sql.SQLException;
+import java.util.List;
 import java.util.Properties;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
@@ -180,6 +181,12 @@ public Properties getClientInfo() {
 
   @Override
   public void close() throws SQLException {
+    // Clean up any open Statements
+    try {
+      AutoCloseables.close(List.copyOf(statementMap.values()));
+    } catch (final Exception e) {
+      throw AvaticaConnection.HELPER.createException(e.getMessage(), e);
+    }
     clientHandler.close();
     if (executorService != null) {
       executorService.shutdown();