[improve][test] Cover reverse equality for topic message IDs

[hiSandog]

Motivation

testBatchMessageIdImplCompareToTopicMessageId repeated the same reverse-order assertion, leaving the corresponding equality case unchecked.

Modifications

Replace the duplicate assertion with a reverse comparison between the topic message ID and the equivalent batch message ID (batchIndex = -1).

Verifying this change

• git diff --check
• Not run: ./gradlew :pulsar-client-original:test -PtestRetryCount=0 --tests org.apache.pulsar.client.impl.MessageIdCompareToTest could not start because this environment has no Java runtime.\n\n### Does this pull request potentially affect one of the following parts:\n\n- [ ] Dependencies (add or upgrade a dependency)\n- [ ] The public API\n- [ ] The schema\n- [ ] The default values of configurations\n- [ ] The threading model\n- [ ] The binary protocol\n- [ ] The REST endpoints\n- [ ] The admin CLI options\n- [ ] The metrics\n- [ ] Anything that affects deployment