tests(iroh-net): Make dht_discovery_smoke test less flaky (#2884)

## Description

This test had a hardcoded sleep(1) in there, which is a recipe for
flaky tests on CI.  Write this more defensively.


## Breaking Changes

<!-- Optional, if there are any breaking changes document them,
including how to migrate older code. -->

## Notes & open questions

I'm kind of tempted to also remove the flaky marker, but who knows.

## Change checklist

- [x] Self-review.
- [x] Documentation updates following the [style
guide](https://rust-lang.github.io/rfcs/1574-more-api-documentation-conventions.html#appendix-a-full-conventions-text),
if relevant.
- [x] Tests if relevant.
- [x] All breaking changes documented.

Author: flub

iroh-net/src/discovery/pkarr/dht.rs

@@ -413,7 +413,7 @@ mod tests {
     #[tokio::test]
     #[ignore = "flaky"]
     async fn dht_discovery_smoke() -> TestResult {
-        let _ = tracing_subscriber::fmt::try_init();
+        let _logging_guard = iroh_test::logging::setup();
         let ep = crate::Endpoint::builder().bind().await?;
         let secret = ep.secret_key().clone();
         let testnet = mainline::dht::Testnet::new(2);
@@ -438,19 +438,27 @@ mod tests {
         });
 
         // publish is fire and forget, so we have no way to wait until it is done.
-        tokio::time::sleep(Duration::from_secs(1)).await;
-        let items = discovery
-            .resolve(ep, secret.public())
-            .unwrap()
-            .collect::<Vec<_>>()
-            .await;
-        let mut found_relay_urls = BTreeSet::new();
-        for item in items.into_iter().flatten() {
-            if let Some(url) = item.addr_info.relay_url {
-                found_relay_urls.insert(url);
+        tokio::time::timeout(Duration::from_secs(30), async move {
+            loop {
+                tokio::time::sleep(Duration::from_millis(200)).await;
+                let mut found_relay_urls = BTreeSet::new();
+                let items = discovery
+                    .resolve(ep.clone(), secret.public())
+                    .unwrap()
+                    .collect::<Vec<_>>()
+                    .await;
+                for item in items.into_iter().flatten() {
+                    if let Some(url) = item.addr_info.relay_url {
+                        found_relay_urls.insert(url);
+                    }
+                }
+                if found_relay_urls.contains(&relay_url) {
+                    break;
+                }
             }
-        }
-        assert!(found_relay_urls.contains(&relay_url));
+        })
+        .await
+        .expect("timeout, relay_url not found on DHT");
         Ok(())
     }
 }