[eng 1944] Ensure/test pgvector compatibility

[conniedonahue]

Changes:

• Adds the pgvector plugin to the library and tests a few functions using vector search
  • note: I allow for earlier versions of numpy if the user is on python <3.10.
• Adds an optional embeddings field to the Document model
• Updates the test setup so that we pull from a pgvector-compatible postgres image

Some things for separate tickets:

• see if we can add stubs for proper Vector typing
  • I gave it a go before deciding to break it off for later -- it was a bit daunting!
  • currently, all of the embeddings functions (e.g. l2_distance) are greyed out // return "Any"
• add overloads to select like we did with query (just noting this hasn't been done yet)

[Copilot]

Pull Request Overview

Adds pgvector support to the library and updates tests to verify vector-based search works under Oso authorization.

• Introduces an optional embedding field on Document backed by pgvector
• Updates test setup to use a pgvector-enabled Postgres image and create the extension
• Adds numerous tests exercising L2, cosine, and inner-product searches via both ORM and Core APIs

Comments suppressed due to low confidence (1)

[vrama628]

nice! Left a few non-blocking comments about whether certain things are necessary

[vrama628]

what's the purpose of specifying 2.1.0 for >=3.10?

[conniedonahue]

This is to ensure compatibility with our lowest accepted python version (3.9) and the latest python version (3.13.5). I ran python on both of these versions while testing. Essentially:

• pgvector requires numpy
• Numpy drops support for 3.9 at 2.1.0
• the highest version of numpy that supports 3.9, 2.0.1 supports up to 3.12, so not 3.13+ :(
• any Python users at 3.13+ would have to use a more recent numpy version.

I thought we might as well use 2.1+ for 3.10, and I carved out this earlier version of numpy for applications python 3.9.

I'll test manually, but I'll see if i can up the version of the python 3.9 version of numpy to 2.0.1:

numpy = [
    { version = ">=1.21.0,<2.1.0", python = "<3.10" },
    { version = ">=2.1.0", python = ">=3.10" },
]