feat(ser): tuple structs support for sql serializer

[marcin-ptaszynski]

Summary

Support for serializing Tuple Structs in the same way as Tuples.

Checklist

Delete items not relevant to your PR:

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided so that we can include it in CHANGELOG later
• For significant changes, documentation in README and https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials

[Copilot]

Pull request overview

This PR adds support for serializing tuple structs in the SQL serializer by treating them the same way as tuples, wrapping their fields in parentheses and separating them with commas.

Changes:

• Updated SqlSerializer to use SqlListSerializer for tuple structs instead of Impossible
• Implemented SerializeTupleStruct trait for SqlListSerializer
• Added test coverage for tuple struct serialization and removed the old test that expected tuple structs to error

---

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