[Enhancement]: Connection GC

[IHEII]

Enhancement

There are serval problems in rpc::Connection garbage collection now.

1. Connection::cancel_requests() duplicated used
2. Connection.active is useless
3. Another way to close the ConnectionSender/Reader/Connection gracefully. The reason why we use shutdown() to close the connection is that we have to use send(closepoison_packet).await to close ConnectionSender. I guess the oneshot::channel or active mentioned before could help to close the ConnectionSender. If we don't send the packet in close() asynchrony, we could implement a common way to drop/close the connection synchrony.