Add enable_time() when worker_threads="auto"

[lxb007981]

Since tokio::time::sleep is used in accept(), we need to add enable_time() in the runtime builder.

But I didn't get the idea why we chose to sleep here? In the current implementation, every time when tcp_socket.accept() is called, it will likely waste some time, return an Err and leave a trace message. If the listeners are many, it might harm the responsiveness. Maybe the better way is to spawn a separate task per listener to call listener.accept(), and see who comes first? Like using futures:future:select_all. Or even simpler, to only support the case with one single listener, like speedtest-go did. Correct me if I'm wrong. Thank you!

[SudoDios]

@lxb007981
You are very accurate 👏
It was because the iteration remains active. But it can probably be implemented better.
I am a bit busy these few days; Some places need cleaning

[SudoDios]

like speedtest-go did

The librespeed-go version does not support multiple listeners.
But here it is possible