Building a better testing experience for Workflows, our durable execution engine for multi-step applications

What this post added

Introduced new testing APIs (`introspectWorkflowInstance`, `introspectWorkflow`) within the `cloudflare:test` module for Workflows, enabling granular, isolated, and offline testing. These APIs leverage `vitest-pool-workers` and `workerd` to allow developers to mock step results and events, improving debugging and reducing friction in adopting Workflows. The implementation details the use of privileged local-only APIs and Remote Procedure Calls (RPC) to interact with the Workflow Engine DOs without invasive changes to Miniflare or vitest-pool-workers.