Shutdown gets stuck sometimes

[sebadob]

This is one of the known issues I mentioned in the readme.

The Client::shutdown() can get stuck at the very last step. I have not found a reason for this yet. Because this is just a tokio::time::sleep().await, which is something where it should never be able to even get stuck at all, I am not sure if the reason has to do something with the test setup, because I did not see it in production for a long time after some tweaks to the shutdown routine.

If you however see hiqlite getting stuck on shutdown, please let me know about this.
I have added info logs after each of the shutdown steps for better debugging this in the wild, until it is solved.

In tests, while the test context is confusing sometimes because it shares static memory and so on (everything is started from the same process), the very last log entry from the procedure is

hiqlite::client::mgmt: Waiting 5 additional seconds before shutting down

If someone sees this and it still does not shut down after 5 seconds, this may be a tokio bug somehow. Please let me know in this case.