only collect topology when peers changed

exo/orchestration/standard_node.py

@@ -374,8 +374,8 @@ class StandardNode(Node):
       try:
         did_peers_change = await self.update_peers()
         if DEBUG >= 2: print(f"{did_peers_change=}")
-        await self.collect_topology(set())
         if did_peers_change:
+          await self.collect_topology(set())
           await self.select_best_inference_engine()
       except Exception as e:
         print(f"Error collecting topology: {e}")