Bug: HNSW index fails if initial insert has doc id > 24999

[etiennedi]

Problem

Previously it was impossible for a doc id of the initial insert into HNSW to be larger than its size. But since we added the ability to add objects without a vector and introduce the vector later it is now possible to import more than 25,000 objects before ever making use of the HNSW index. In that case, we now need to check if the initial size is large enough and adjust it accordingly.

Goals

• The initial insert will work with any doc id regardless of initial index size
• Add tests to prevent regression

Notes

While we can reproduce this with a stress test, I think we should also be able to reproduce this with a very simple integration test in the adapters/repos/db/vector/hnsw package. A simple insert with doc id 25,000 on an empty index should already reproduce this.