fix: spawn all npcs in already loaded chunks on start (#1255)

### Motivation
When a npc is located in the spawn chunks of the world the npc won't get
spawned. This is caused by the fact that the chunk load event is called
before our plugin is started.

### Modification
Spawned all npcs on start that are located in already loaded chunks

### Result
No non existing npcs

modules/npcs/src/main/java/eu/cloudnetservice/modules/npc/platform/bukkit/BukkitPlatformNPCManagement.java

@@ -164,6 +164,18 @@ public BukkitPlatformNPCManagement(
     }, 20, 5);
   }
 
+  @Override
+  public void initialize() {
+    super.initialize();
+
+    // spawn all npcs that are in chunks that were loaded before the plugin was enabled
+    for (var entity : this.trackedEntities.values()) {
+      if (entity.canSpawn()) {
+        entity.spawn();
+      }
+    }
+  }
+
   @Override
   protected @NonNull PlatformSelectorEntity<Location, Player, ItemStack, Inventory, Scoreboard> createSelectorEntity(
     @NonNull NPC base