tests: Add newline handling to slt when multiline is not specified

[ggevay]

The first commit changes the CODEOWNERS of /src/sqllogictest from @MaterializeInc/adapter to @MaterializeInc/testing. (But let me know if there was a good reason to have the Adapter team be the owner.) Edit: Also added myself, as discussed in DMs.

The second commit fixes a minor bug in space handling in slt in colnames.

The third commit is the main thing, which adds newline handling to slt result values, even when multiline is not specified. We use the replacement character trick to avoid newlines inside result values conflicting with newlines that are for field or row separation: when rewriting, we replace newlines with ⏎; when parsing, we replace ⏎ with newlines.

The motivation is that I'd like to have this feature for my next PR, which will make SHOW CREATE ... pretty-print its output, adding newlines. We have a gazillion tests that call SHOW CREATE, and it would be painful to change all of them to use multiline, especially that they have multi-column outputs, which, I think, is not really supported with multiline.

(I've added lts-backport-v25.1, because the SHOW CREATE PR will need to be backported, because mzexplore will rely on that, and mzexplore is part of the self-managed debug tool.)

Motivation

• This PR adds a feature that has not yet been specified.

Tips for reviewer

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.

[def-]

The first commit changes the CODEOWNERS of /src/sqllogictest from @MaterializeInc/adapter to @MaterializeInc/testing. (But let me know if there was a good reason to have the Adapter team be the owner.)

Generally we haven't written many SLT tests in the testing team, and more focused on higher level frameworks. It still makes sense to review test changes though.