Build a Webhook Handler

Write a production-ready webhook handler for the following:

Service sending the webhook: [e.g. Stripe / GitHub / Shopify / custom service]
Framework: [e.g. Next.js API route / Express / FastAPI / Go net/http]
Events to handle: [list the specific event types — e.g. payment.succeeded / push / order.created]
What to do with each event: [describe the action for each event type]
Signature verification: [yes — describe the method / no]

Implementation must include:
1. Route handler with raw body parsing (required for signature verification)
2. Signature verification with timing-safe comparison
3. Event type router — clean switch/if structure to handle each event
4. Idempotency: how to handle duplicate deliveries
5. Error handling: what to return on verification failure vs. processing failure
6. Logging: what to log for debugging and audit trail
7. Async processing: if events trigger slow operations, how to respond quickly and process in background
8. Retry handling: what HTTP status to return so the sender knows to retry vs. not

Include a test for the signature verification logic.