Support async adapters

[aviralgarg05]

Summary

Add support for async adapters to handle agents that use async/await.

Tasks

• Create AsyncBaseAdapter with async def execute().
• Update run_suite() to detect and await async adapters.
• Add example async adapter in docs/templates.
• Ensure backwards compatibility with sync adapters.

Acceptance criteria

• Async adapters work with asyncio.run() or event loop.
• Mixed sync/async scenarios in same suite work.
• Tests cover async execution path.