feat(lapis): also handle SILO returning arrow date values

[Taepper]

For testing, we will first need to handle sending saneql queries, which has been finished in #1682

Now this PR adds handling of returned arrow batches that also contain date arrays

PR Checklist

- [ ] All necessary documentation has been adapted.
- [ ] All necessary changes are explained in the llms.txt.

• The implemented feature is covered by an appropriate test.

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
lapis	Ready	Preview, Comment	May 27, 2026 6:34am

[Copilot]

Pull request overview

Updates the SILO Arrow response handling so LAPIS can correctly serialize Arrow date32/day values into JSON, preventing unexpected stringification of raw day offsets.

Changes:

• Add explicit handling for DateDayVector (Arrow date32) in fieldValueAsJsonNode to return an ISO-8601 date string.
• Add the required Arrow vector import (DateDayVector).

---

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

[fengelniederhammer]

What Copilot said. The SiloClientTest tests the deserialization of responses, I think that's were we should also test this change.

Otherwise looks good, the e2e are back to green!

[fengelniederhammer]

Thanks! :)