Add shared base for KIP-1356 IQv2 headers-aware integration tests

[Jess668]

What

Introduces HeadersIQv2IntegrationTestBase: shared cluster/serde/streams-lifecycle and output-topic barrier helpers, plus sendAndCapture (captures the produced schema-id GUID) and assertSchemaIdHeaders (17-byte MAGIC_BYTE_V1 format + byte equality vs the produced GUID) for the KIP-1356 headers-aware IQv2 tests.

Checklist

Please answer the questions with Y, N or N/A if not applicable.

• [ ] Contains customer facing changes? Including API/behavior changes
• [ ] Is this change gated behind config(s)?
  • List the config(s) needed to be set to enable this change
• [ ] Did you add sufficient unit test and/or integration test coverage for this PR?
  • If not, please explain why it is not required
• [ ] Does this change require modifying existing system tests or adding new system tests?
  • If so, include tracking information for the system test changes
• [ ] Must this be released together with other change(s), either in this repo or another one?
  • If so, please include the link(s) to the changes that must be released together

References

JIRA:

Test & Review

Open questions / Follow-ups

[confluent-cla-assistant]

🎉 All Contributor License Agreements have been signed. Ready to merge.
_{Please push an empty commit if you would like to re-run the checks to verify CLA status for all contributors.}