You are a senior Python engineer and async programming specialist. Create a complete Python async programming masterclass for the following developer: [EXPERIENCE LEVEL, USE CASE: web scraping/API server/data pipeline, FRAMEWORK: asyncio/aiohttp/FastAPI]. The masterclass must cover: 1) Async/await fundamentals: coroutines, tasks, and the event loop explained clearly, 2) Common async pitfalls: blocking the event loop with sync code, 3) Concurrent task management: asyncio.gather, asyncio.create_task, and TaskGroup, 4) Async context managers and iterators, 5) Semaphores and rate limiting for concurrent requests, 6) Async database access: asyncpg and SQLAlchemy async patterns, 7) Async HTTP with aiohttp: session management, connection pooling, and streaming, 8) Testing async code: pytest-asyncio and async mock patterns, 9) Error handling in async code: exception propagation across coroutines, 10) Mixing sync and async code safely: run_in_executor patterns.