Improved Cloudflare Workers testing via Vitest and workerd

This post introduces a new Vitest integration for Cloudflare Workers, allowing developers to write unit and integration tests that execute directly within the `workerd` runtime. This enables testing of Worker code, interactions with Cloudflare products (KV, R2, D1, Queues, Service Bindings), and Cron Triggers. The integration uses Vitest's custom pools feature to run the test runner within `workerd`, communicating via WebSockets. It also provides features like hot-module-reloading and per-test isolated storage.