tests: Introduce SQLancer++

[def-]

This is based on Gabor's PR #34892. I'll rebase with only the second commit after it's been merged.

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.

[ggevay]

The Postgres CDC CI fail is from #34892 first commit, which I've now fixed in the second commit of that PR.

[ggevay]

Thank you! It seems it's very effective at finding issues!

[def-]

Yep, I'll just wait until your PR is merged before merging this!

[def-]

Thank you! It seems it's very effective at finding issues!

Mostly not the kinds of issues it was trying to find though! Only a select few correctness issues.

The panics were mostly found because it seems to have a worse idea of types than SQLsmith/parallel-workload currently and also has some extra syntax.