[AI-8th] Fixes duplicate publisher registration detection in DefaultRegistryClient

[pmupkin]

This PR(Related issue #47) fixes duplicate publisher registration detection in DefaultRegistryClient.

DefaultRegistryClient uses PublisherRegistration as the key in registrationPublisherMap, but PublisherRegistration did not override equals and hashCode, so two registrations with the same registration attributes were treated as different keys. As a result, duplicate publisher registrations could bypass the existing duplicate check.

Changes

• Implemented equals and hashCode for PublisherRegistration.
• Added unit coverage for PublisherRegistration equality and hash code behavior.
• Added a DefaultRegistryClient test to verify duplicate publisher registration now throws DuplicateException.
• Updated the multi-unregister test to use different publisher groups when registering multiple publishers with the same dataId.

[huanglongchao]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

🤖 Generated with Claude Code

_{- If this code review was useful, please react with 👍. Otherwise, react with 👎.}