Expand examples/ with more real-world scenarios

[elijahr]

The examples/ directory has 5 examples. Add more realistic integration testing scenarios:

• Testing a FastAPI app with mocked database and HTTP calls
• Testing a Celery task with mocked Redis and external API
• Testing a data pipeline with mocked S3 and database
• Testing WebSocket communication patterns

Each example should be a runnable, self-contained test file with inline comments explaining the patterns.