Support Cython 3

[davispuh]

Description

Cython 0.x doesn't support Python 3.13 so for that need to update to Cython 3

Types of change

Update to build with Cython 3

Checklist

• I confirm that I have the right to submit this contribution under the project's MIT license.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[honnibal]

I've been working on this and it's actually very difficult. Cython 3 forces from __future__ import annotations, which messes with Pydantic. Separately I'm also trying to get Pydantic support for Pydantic v2 and there's a lot of problems.