Offload synchronous actions in ctx.run via asyncio.to_thread to prevent event loop blocking

[ouatu-ro]

This change ensures that:

• Sync functions passed to ctx.run are executed in a background thread.
• The event loop remains unblocked, maintaining the performance of concurrent handlers.
• The behavior is consistent with other async frameworks such as FastAPI.

Related to #46

[igalshilman]

thanks @ouatu-ro 🎉

LGTM!