Track Vercel request IDs on workflow events for logs correlation

[karthikscale3]

Summary

• Captures the x-vercel-id header from incoming VQS requests using AsyncLocalStorage and threads it through the entire workflow and step execution pipeline
• Every world.events.create() call now forwards the request ID as vercelId in the event creation payload, enabling correlation between Vercel platform request logs and workflow events
• Adds requestId to the CreateEventParams interface (@workflow/world) and the queue handler metadata, making this available to all world implementations

Changes

• @workflow/world: Added requestId to CreateEventParams and queue handler metadata types
• @workflow/world-vercel: Extracts x-vercel-id from the incoming request header via AsyncLocalStorage, passes it as vercelId in event creation POST bodies
• @workflow/core: Plumbs requestId from queue metadata through the runtime, step handler, and suspension handler to all event creation calls (run_started, run_completed, run_failed, step_started, step_completed, step_failed, step_retried, hooks, waits)

Test plan

• Verify x-vercel-id header is correctly captured from VQS callback requests
• Confirm vercelId appears in event creation payloads to workflow-server
• Validate existing e2e tests pass (no behavioral change, additive only)