Server::run should return ! (never type)

[ia0]

Is your feature request related to a problem? Please describe.
One has to write unreachable!() after server.run().await.

Describe the solution you'd like
I want Server::run() to return ! (never type):

pub async fn run(self, addr: impl Into<SocketAddr>) -> !;

Or, if run() may actually return (although its documentation says it doesn't), then update the documentation to explain when it can return.

Describe alternatives you've considered
Writing unreachable!() manually.