Test the opportunity to not abort timed out get_slice, but instead run a race with retried attempt

[fulmicoton]

In #5466 we introduced aggressive timeout/retries to improve latency.
We could avoid abort attempts on timeout and instead run a race with the new attempts.

As suggested by @trinity-1686a

/// Downloads a slice of a file from the storage, and returns an in memory buffer
    async fn get_slice(&self, path: &Path, range: Range<usize>) -> StorageResult<OwnedBytes> {
        let mut futures_unordered = FuturesUnordered::new();
        let num_bytes = range.len();

        for (attempt_id, timeout_duration) in self
            .storage_timeout_policy
            .compute_timeout(num_bytes)
            .enumerate()
        {
            let get_slice_fut = self.underlying.get_slice(path, range.clone());
            futures_unordered.push(get_slice_fut);
            match tokio::time::timeout(timeout_duration, futures_unordered.next()).await {
                Ok(Some(result)) => {
                    crate::STORAGE_METRICS
                        .get_slice_timeout_successes
                        .get(attempt_id)
                        .or(crate::STORAGE_METRICS.get_slice_timeout_successes.last())
                        .unwrap()
                        .inc();
                    return result;
                }
                Ok(None) => {
                    // ..
                }
                Err(_elapsed) => {
                    rate_limited_info!(limit_per_min=60, num_bytes=num_bytes, path=%path.display(), timeout_secs=timeout_duration.as_secs_f32(), "get timeout elapsed");
                    continue;
                }
            }
        }
        rate_limited_warn!(limit_per_min=60, num_bytes=num_bytes, path=%path.display(), "all get_slice attempts timeouted");
        crate::STORAGE_METRICS.get_slice_timeout_all_timeouts.inc();
        return Err(
            StorageErrorKind::Timeout.with_error(anyhow::anyhow!("internal timeout on get_slice"))
        );
    }