fix: use await asyncio.sleep instead of blocking time.sleep in async voter retry

[kratos0718]

Summary

In jina/orchestrate/deployments/__init__.py, the voter-add retry loop runs inside an async function (it awaits async_call_add_voter), but its back-off uses a blocking time.sleep(2.0):

success = await async_call_add_voter(leader, str(replica_id), voter_address)
if success:
    break
else:
    time.sleep(2.0)   # blocks the event loop

time.sleep blocks the entire event loop for its duration — 2s per retry, up to ~10s across the 5 attempts. While it sleeps, every other coroutine on the loop is frozen.

Fix

Use await asyncio.sleep(2.0), which backs off without blocking the loop. asyncio is already imported; behavior is otherwise identical.

• Compiles cleanly (python -m py_compile).