Implement aggressive shape hardening mode and related tests

src/ip_tracker.rs

@@ -22,7 +22,7 @@ pub struct UserIpTracker {
     limit_mode: Arc<RwLock<UserMaxUniqueIpsMode>>,
     limit_window: Arc<RwLock<Duration>>,
     last_compact_epoch_secs: Arc<AtomicU64>,
-    pub(crate) cleanup_queue: Arc<Mutex<Vec<(String, IpAddr)>>>,
+    cleanup_queue: Arc<Mutex<Vec<(String, IpAddr)>>>,
     cleanup_drain_lock: Arc<AsyncMutex<()>>,
 }
 
@@ -57,6 +57,19 @@ impl UserIpTracker {
         }
     }
 
+    #[cfg(test)]
+    pub(crate) fn cleanup_queue_len_for_tests(&self) -> usize {
+        self.cleanup_queue
+            .lock()
+            .unwrap_or_else(|poisoned| poisoned.into_inner())
+            .len()
+    }
+
+    #[cfg(test)]
+    pub(crate) fn cleanup_queue_mutex_for_tests(&self) -> Arc<Mutex<Vec<(String, IpAddr)>>> {
+        Arc::clone(&self.cleanup_queue)
+    }
+
     pub(crate) async fn drain_cleanup_queue(&self) {
         // Serialize queue draining and active-IP mutation so check-and-add cannot
         // observe stale active entries that are already queued for removal.