NPC refactor (#10122)

Co-authored-by: metalgearsloth <metalgearsloth@gmail.com>

Content.Server/NPC/Systems/NPCPerceptionSystem.cs

@@ -0,0 +1,13 @@
+namespace Content.Server.NPC.Systems;
+
+/// <summary>
+/// Handles sight + sounds for NPCs.
+/// </summary>
+public sealed partial class NPCPerceptionSystem : EntitySystem
+{
+    public override void Update(float frameTime)
+    {
+        base.Update(frameTime);
+        UpdateRecentlyInjected(frameTime);
+    }
+}