Make some of the stream tests more robust against bad timeouts (#12271)

# Description

@WindSoilder [reported on
Discord](https://discord.com/channels/601130461678272522/855947301380947968/1221233630093901834)
that some plugin stream tests have been failing on the CI. It seems to
just be a timing thing (probably due to busy CI), so this extends the
amount of time that we can wait for a condition to be true.

# User-Facing Changes
None

# Tests + Formatting
- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

crates/nu-plugin/src/plugin/interface/stream/tests.rs

@@ -3,7 +3,7 @@ use std::{
         atomic::{AtomicBool, Ordering::Relaxed},
         mpsc, Arc,
     },
-    time::Duration,
+    time::{Duration, Instant},
 };
 
 use nu_protocol::{ShellError, Value};
@@ -16,6 +16,36 @@ use super::{StreamManager, StreamReader, StreamWriter, StreamWriterSignal, Write
 // slow to complete. 10 ms is a pretty long time
 const WAIT_DURATION: Duration = Duration::from_millis(10);
 
+// Maximum time to wait for a condition to be true
+const MAX_WAIT_DURATION: Duration = Duration::from_millis(500);
+
+/// Wait for a condition to be true, or panic if the duration exceeds MAX_WAIT_DURATION
+#[track_caller]
+fn wait_for_condition(mut cond: impl FnMut() -> bool, message: &str) {
+    // Early check
+    if cond() {
+        return;
+    }
+
+    let start = Instant::now();
+    loop {
+        std::thread::sleep(Duration::from_millis(10));
+
+        if cond() {
+            return;
+        }
+
+        let elapsed = Instant::now().saturating_duration_since(start);
+        if elapsed > MAX_WAIT_DURATION {
+            panic!(
+                "{message}: Waited {:.2}sec, which is more than the maximum of {:.2}sec",
+                elapsed.as_secs_f64(),
+                MAX_WAIT_DURATION.as_secs_f64(),
+            );
+        }
+    }
+}
+
 #[derive(Debug, Clone, Default)]
 struct TestSink(Vec<StreamMessage>);
 
@@ -301,8 +331,7 @@ fn signal_wait_for_drain_blocks_on_unacknowledged() -> Result<(), ShellError> {
         for _ in 0..100 {
             signal.notify_acknowledged()?;
         }
-        std::thread::sleep(WAIT_DURATION);
-        assert!(spawned.is_finished(), "blocked at end");
+        wait_for_condition(|| spawned.is_finished(), "blocked at end");
         spawned.join().unwrap()
     })
 }
@@ -322,8 +351,7 @@ fn signal_wait_for_drain_unblocks_on_dropped() -> Result<(), ShellError> {
         std::thread::sleep(WAIT_DURATION);
         assert!(!spawned.is_finished(), "didn't block");
         signal.set_dropped()?;
-        std::thread::sleep(WAIT_DURATION);
-        assert!(spawned.is_finished(), "still blocked at end");
+        wait_for_condition(|| spawned.is_finished(), "still blocked at end");
         spawned.join().unwrap()
     })
 }