integration: enable vector type tests for ScyllaDB

[wprzytula]

ScyllaDB now supports vector type, so we can enable the vector type tests that were previously ignored for ScyllaDB.

However, there's a bug in Vector implementation (scylladb/scylladb#26704), which makes the tests fail. This PR shall then be merged once the bug is fixed and a new stable release with the fix is available at docker, so the CI gets it.

Pre-review checklist

• I have split my patch into logically separate commits.
• All commit messages clearly explain what they change and why.
• [ ] I added relevant tests for new features and bug fixes.
• All commits compile, pass static checks and pass test.
• PR description sums up the changes and reasons why they should be introduced.
• [ ] I have provided docstrings for the public items that I want to introduce.
• [ ] I have adjusted the documentation in ./docs/source/.
• [ ] I added appropriate Fixes: annotations to PR description.

[Copilot]

Pull Request Overview

This PR enables vector type integration tests for ScyllaDB by updating the conditional compilation attributes. The tests were previously disabled for all ScyllaDB instances but are now only disabled for ScyllaDB Cloud/serverless environments where the version is too old to support vector types.

Key Changes:

• Updated cfg_attr conditions from not(cassandra_tests) to scylla_cloud_tests for vector type tests
• Updated comments to reflect that only serverless ScyllaDB versions lack vector type support

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[github-actions]

cargo semver-checks found no API-breaking changes in this PR.
Checked commit: 796d537

[Lorak-mmk]

If we knew that it would take long to fix, then I think it would make sense to split test into part that works with Scylla and the one that doesn't.
I see it has "release blocker" tag, so we can probably just wait for the fix as you proposed.

[Lorak-mmk]

Looks good, we can merge after Scylla fixes the bug.