Add KIP-1356 IQv2 headers-aware KV-store integration tests

[Jess668]

What

TimestampedKeyValueStoreWithHeadersIQv2IntegrationTest (11 tests): point
(hit/skipCache/cache-hit-before-flush/tombstone lifecycle) and range
(withRange/lower/upper/noBounds, asc/desc incl. bounded descending, scan),
plus restore-from-changelog and multi-partition scan. Extends
HeadersIQv2IntegrationTestBase.

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

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