Optimize pipe net appearance updating. (#6469)

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>

Content.Server/NodeContainer/EntitySystems/NodeGroupSystem.cs

@@ -245,14 +245,22 @@ namespace Content.Server.NodeContainer.EntitySystems
             _toRemake.Clear();
             _toRemove.Clear();
 
+            // notify entities that node groups have been updated, so they can do things like update their visuals.
+            HashSet<EntityUid> entities = new();
             foreach (var group in newGroups)
             {
                 foreach (var node in group.Nodes)
                 {
-                    node.OnPostRebuild();
+                    entities.Add(node.Owner);
                 }
             }
 
+            foreach (var uid in entities)
+            {
+                var ev = new NodeGroupsRebuilt(uid);
+                RaiseLocalEvent(uid, ref ev, true);
+            }
+
             _sawmill.Debug($"Updated node groups in {sw.Elapsed.TotalMilliseconds}ms. {newGroups.Count} new groups, {refloodCount} nodes processed.");
         }
 
@@ -402,4 +410,19 @@ namespace Content.Server.NodeContainer.EntitySystems
             };
         }
     }
+
+    /// <summary>
+    ///     Event raised after node groups have been updated. Directed at any entity with a <see
+    ///     cref="NodeContainerComponent"/> that had a relevant node.
+    /// </summary>
+    [ByRefEvent]
+    public readonly struct NodeGroupsRebuilt
+    {
+        public readonly EntityUid NodeOwner;
+
+        public NodeGroupsRebuilt(EntityUid nodeOwner)
+        {
+            NodeOwner = nodeOwner;
+        }
+    }
 }