SQL store hardening

The SQL store currently works well, but we can do a bunch of small upgrades to harden it and prepare it for a stable release. Some of these can be spun off into their own issues but for now I'm dumping what I've compiled here. Each section is meant to be a guide and more can be investigated on each of them:

- Migrations
- Schema
- Indexes and queries
- Connection handling
- Errors
- Internal cleanup

I think we can also look into minimizing the `Store` trait interface, and add blanket implementation for a some subset of the methods

The issue outlines several areas for hardening the SQL store: migrations, schema, indexes, queries, connection handling, errors, and internal cleanup. Start by examining the SQL store implementation in the codebase, likely under a directory like `store/` or `sql_store/`. Look for the `Store` trait definition and its current implementations. Review existing migrations and schema definitions to understand the current structure. The goal is to identify specific, small improvements within each area that can be made independently.

Written by the indexing model from the issue text.