private String getOffset(MessageId msgId) {
            return Base64.getEncoder().encodeToString(msgId.toByteArray());
        }
put the received msg to onFinished method

@param messageRecords {@link List}
inlong-sdk/sort-sdk/src/main/java/org/apache/inlong/sdk/sort/fetcher/pulsar/PulsarMultiTopicsFetcher.java