Adapter: Implement Postgres adapter

[mattpocock]

Overview

Create Postgres adapter for production-grade, scalable storage.

Characteristics

• Production-grade relational DB
• Best for large teams, high volume
• Advanced querying, scalability
• Connect to existing Postgres infrastructure

Implementation

• Create src/adapters/postgres.ts
• Implement EvaliteAdapter interface using postgres client (e.g., pg or postgres)
• Create schema migration for tables (runs, evals, results, scores, traces)
• Support connection config (url, pool settings, etc.)
• Export createPostgresAdapter(opts) helper
• Add tests using multi-adapter test suite
• Document usage examples

Configuration

interface PostgresAdapterOpts {
  connectionString?: string;
  host?: string;
  port?: number;
  database?: string;
  user?: string;
  password?: string;
  ssl?: boolean;
  maxConnections?: number;
}

Related

Part of adapter API refinement (#218)

[Neil-gotcha-back]

@mattpocock Neil from the Discord here - I have a working postgres adapter in my local environment, I need to clean it up before sharing it, I'll probably use it for a few days to make sure it's stable.

Did you want me to open a PR with the above?

[mattpocock]

@Neil-gotcha-back Sounds great! Even a gist would be great for prompting Claude to get it done - it's pretty great at building to existing interfaces and we've already got a 100% test suite.