Display "Elapsed" errors from Timeouts as "timeout"

[teor2345]

Is your feature request related to a problem? Please describe.

Currently, when Zebra encounters a timeout, it debug-prints the Elapsed error, which displays the text:

... Elapsed() ...

But these errors would be a lot more readable if they were displayed as:

... timeout elapsed ...

Describe the solution you'd like

We should print tokio::Timeout's Elapsed errors as timeout elapsed.

But I don't know how to do that easily - maybe we need a wrapper around the Timeout future to modify its error display and debug impls?

We'll also need to make sure there isn't any code that specifically checks for the Elapsed error, or the string Elapsed.

Describe alternatives you've considered

Do nothing.

Explain what Elapsed means in Zebra's documentation.

Related Issues

Noted in #1535, but it's been an issue for a while.

[teor2345]

Would be nice, but we've never actually needed this.