Add fastapi-cicd example with functional testing

[andyreagan]

Summary

• Adds a new fastapi-cicd example demonstrating functional testing for Lambda Web Adapter applications
• Includes tests that run both Docker containers directly and via SAM local
• Provides a GitHub Actions workflow for CI/CD (included as reference, won't run from examples folder)
• Uses modern Python tooling with uv for fast, reproducible dependency management

Features

• FastAPI application with / and /health endpoints
• Test infrastructure using pytest with retry logic for server startup
• Docker testing validates the app works as a standalone web server
• SAM local testing validates the app works in the Lambda runtime with the Web Adapter

Links

Full working repository with CI/CD: https://github.com/andyreagan/aws-lamdba-web-adapter-functional-testing

Test plan

• Verify example builds: cd examples/fastapi-cicd && docker build -t hello-world-lambda .
• Verify SAM build: sam build
• Verify tests pass: uv sync && uv run pytest tests/test_functional.py -v