Implement VSETATTR command for vector set attribute updates

[Copilot]

Implements VSETATTR command to update attributes on existing vector elements without modifying the vector data itself.

Implementation Details

• Command handler: Added VectorSetUpdateAttributes() in VectorStoreOps.cs that acquires read lock on the vector index and calls VectorManager.TryUpdateElementAttributes()
• Native integration: Calls NativeDiskANNMethods.set_attribute() to update attributes in the DiskANN index
• Replication support: Triggers manual replication via ReplicateVectorUpdateAttributes() on successful updates
• RMW handlers: Added cases in InitialUpdater, InPlaceUpdater, and CopyUpdater for replication path (assertions ensure only replication triggers these paths)

Usage

VSETATTR key element '{"category": "updated", "score": 95}'

Architecture Note

VSETATTR and VADD use separate native methods for attribute writes:

• VADD → insert() - writes attributes during element insertion
• VSETATTR → set_attribute() - updates attributes on existing elements

No shared attribute write path exists between the commands.

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.