Purpose of the change

Add embedded implementations of VectorStore.

Description

Based on #1291.

One is based on SQLite + sqlite-vec (https://github.com/asg017/sqlite-vec).

• sqlite-vec only works with SQLite that allows loading extensions, and does not support ANN yet.

One is based on SQLite + Vector Search Engine e.g.

• hnswlib (https://github.com/nmslib/hnswlib)
• USearch (https://github.com/unum-cloud/usearch)
• also considered FAISS but it conflicts with PyTorch and it does not support deletion well

Notes:

• sqlite-vec is not usable OotB when the Python installation does not support loading SQLite extensions. This may be hard to debug for consumers.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (does not change functionality, e.g., code style improvements, linting)
• Documentation update
• Project Maintenance (updates to build scripts, CI, etc., that do not affect the main project)
• Security (improves security without changing functionality)

How Has This Been Tested?

• Unit Test
• Integration Test
• End-to-end Test
• Test Script (please provide)
• Manual verification (list step-by-step instructions)

Checklist

[Please delete options that are not relevant.]

• I have signed the commit(s) within this pull request
• My code follows the style guidelines of this project (See STYLE_GUIDE.md)
• I have performed a self-review of my own code
• I have commented my code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added unit tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings

Maintainer Checklist

• Confirmed all checks passed
• Contributor has signed the commit(s)
• Reviewed the code
• Run, Tested, and Verified the change(s) work as expected