Fix blocking std::thread::sleep in async runtime

[QuantumFUD]

Issue:

wait_for_readiness is an async function but used std::thread::sleep, which blocks the Tokio runtime. Since this function is awaited from main, blocking calls pause the entire async executor for 5 seconds on each retry.

Fix:

Replaced std::thread::sleep with tokio::time::sleep(...).await and removed the blocking import and closure.

Impact:

The function is now fully non-blocking and correctly cooperates with the async runtime. This prevents unnecessary executor blocking and improves overall responsiveness.

[emmajam]

this its negligible impact but good hygiene - will merge