Feature: improve filtered search with ACORN-1

[cpegeric]

Describe what you are looking for

add ACORN-1 for filtered search for improvement.

To implement ACORN-1, when visiting a node in the HNSW search, we take the neighbors and 2-hop neighbors of the node, and for those that pass the filter, computes their distance to the query vector to see if they are relevant.

https://arxiv.org/abs/2403.04871

https://blog.vespa.ai/additions-to-hnsw/

Proposed PR created: #673

Can you contribute to the implementation?

• [ ] I can contribute

Is your feature request specific to a certain interface?

It applies to everything

Contact Details

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Is there an existing issue for this?

• [x] I have searched the existing issues

Code of Conduct

• [x] I agree to follow this project's Code of Conduct