I hate `log_error`. A better way to do this would be to not reuse the
same error type literally everywhere, so you could distinguish, in
`crate::service::sending::Service::handle_response`, whether to emit an
event based on which function created the error. Fixing that is a lot
more work, though.
tokio::spawn is a span boundary, the spawned future has no parent span.
For short futures, we simply inherit the current span with
`.in_current_span()`.
For long running futures containing a sleeping infinite loop, we don't
actually want a span on the entire task or even the entire loop body,
both would result in very long spans. Instead, we put the outermost span
(created using #[tracing::instrument] or .instrument()) around the
actual work happening after the sleep, which results in a new root span
being created after every sleep.
This change is fully automated, except the `rustfmt.toml` changes and
a few clippy directives to allow specific functions with too many lines
because they are longer now.
I would've preferred to factor these out into their own functions, but
unfortunately the inner type of the `FuturesUnordered` is unnameable.
`Box` or TAIT would help, but the former has a performance cost and the
latter doesn't exist on stable yet.
