uasync: add event loop stall detection (warn if >10ms between poll entries)

lib/u_async.c

@@ -984,6 +984,13 @@ void uasync_poll(struct UASYNC* ua, int timeout_tb) {
     if (!ua) return;
     if (!ua->sockets || !ua->timeout_heap) return;
 
+    uint64_t now_us_poll_entry = get_time_us();
+    if (ua->last_poll_entry_us && now_us_poll_entry - ua->last_poll_entry_us > 10000) {
+        DEBUG_WARN(DEBUG_CATEGORY_UASYNC, "Event loop stall: %lluus since last poll entry",
+                   (unsigned long long)(now_us_poll_entry - ua->last_poll_entry_us));
+    }
+    ua->last_poll_entry_us = now_us_poll_entry;
+
     DEBUG_DEBUG(DEBUG_CATEGORY_UASYNC, "poll(%d sockets, %zu timers, timeout=%d.%dms)",
                 ua->sockets->count, ua->timeout_heap->size, timeout_tb >= 0 ? timeout_tb / 10000 : -1,
                 timeout_tb >= 0 ? (timeout_tb % 10000) / 10 : 0);    
@@ -1320,6 +1327,7 @@ struct UASYNC* uasync_create(void) {
     ua->posted_tasks_head = NULL;
     ua->immediate_queue_head = NULL;
     ua->immediate_queue_tail = NULL;
+    ua->last_poll_entry_us = 0;
 
     DEBUG_DEBUG(DEBUG_CATEGORY_ETCP, "Creating SA...");
     ua->sockets = socket_array_create(16);

lib/u_async.h

@@ -75,6 +75,7 @@ struct UASYNC {
     pthread_mutex_t posted_lock;
 #endif
     volatile sig_atomic_t stop;
+    uint64_t last_poll_entry_us;
 };
 
 // Type definitions