pulsar: support debezium protocol

[HGHNice]

What problem does this PR solve?

Issue Number: close #5056

The Pulsar sink currently only supports canal-json. Users who consume
TiCDC events via Pulsar with Debezium-compatible consumers (e.g. Flink CDC)
have no way to use the standard Debezium message format.

What is changed and how it works?

• Extend IsPulsarSupportedProtocols() in pkg/config/sink_protocol.go
  to include ProtocolDebezium.
• Update the error message in downstreamadapter/sink/pulsar/helper.go
  to reflect the expanded protocol list.
• The Debezium codec is already fully implemented and shared with the Kafka
  sink via the common codec builder, so no additional encoding logic is needed.
• Add unit test TestIsPulsarSupportedProtocols.

Check List

Tests

• Unit test

Questions

Will it cause performance regression or break compatibility?

No. Existing canal-json behavior is unchanged.

Do you need to update user documentation, design documentation or monitoring documentation?

The Pulsar sink docs should note that debezium is now a valid protocol value.

Release note

The Pulsar sink now supports the `debezium` protocol. Set `protocol=debezium`
in the Pulsar sink URI to produce Debezium-format change events.


## Summary by CodeRabbit

## Release Notes

* **New Features**
  * Pulsar sink now supports debezium protocol in addition to canal-json protocol.

* **Tests**
  * Added validation tests for Pulsar sink protocol compatibility.

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[coderabbitai]

📝 Walkthrough

Walkthrough

This PR extends Pulsar sink protocol support from canal-json only to include debezium as well. The validation logic is updated with corresponding test coverage, and user-facing error messages and comments in the Pulsar helper are refreshed to reflect the expanded protocol support.

Changes

Pulsar Debezium Protocol Support

Layer / File(s)	Summary
Protocol validation logic and test pkg/config/sink_protocol.go, pkg/config/sink_protocol_test.go	IsPulsarSupportedProtocols now returns true for both ProtocolCanalJSON and ProtocolDebezium. A new parallel test case validates the function returns true for those two protocols and false for ProtocolAvro, ProtocolOpen, ProtocolSimple, and ProtocolCanal.
Pulsar sink error message and documentation downstreamadapter/sink/pulsar/helper.go	The unsupported protocol error message is updated to list [canal-json, debezium] instead of [canal-json], and an obsolete inline comment claiming Pulsar only supports canal-json is removed.

🎯 1 (Trivial) | ⏱️ ~3 minutes

🐰 A rabbit hops with glee, both canals and bees,
No longer just JSON, now Debezium flows free!
Comments updated, protocols sound true,
Tests verify both—good work through and through! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 20.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: adding Debezium protocol support to the Pulsar sink.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The pull request description follows the required template with all essential sections properly completed including issue number, problem statement, changes explanation, test verification, compatibility assessment, and release notes.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[pingcap-cla-assistant]

All committers have signed the CLA.

[gemini-code-assist]

Code Review

This pull request adds support for the Debezium protocol to the Pulsar sink by updating the protocol validation logic and error messages. Feedback includes a recommendation to replace a hardcoded boolean with a dynamic protocol check in the event router, a request for additional test coverage in existing protocol parsing and string conversion tests, and a minor grammatical correction in a user-facing error message.