fix: use Bukkit API instead of NMS getAllLevels() for world iteration

MinecraftServer.getAllLevels() obfuscated method name changed in 1.21.11.
Switch to using Bukkit.getWorlds() with CraftWorld.getHandle() which is
more stable across version updates.

Author: claude

src/main/java/cf/catworlds/dynamicspigotsetting/utils/ServerHelper.java

@@ -1,7 +1,8 @@
 package cf.catworlds.dynamicspigotsetting.utils;
 
-import net.minecraft.server.MinecraftServer;
 import org.bukkit.Bukkit;
+import org.bukkit.World;
+import org.bukkit.craftbukkit.CraftWorld;
 
 public class ServerHelper {
 
@@ -11,22 +12,28 @@ static public double getTPS() {
 
     @SuppressWarnings("deprecation")
     static public double getItemMerge() {
-        return MinecraftServer.getServer().getAllLevels().iterator().next().spigotConfig.itemMerge;
+        World world = Bukkit.getWorlds().get(0);
+        return ((CraftWorld) world).getHandle().spigotConfig.itemMerge;
     }
 
     @SuppressWarnings("deprecation")
     static public void setItemMerge(double radius) {
-        MinecraftServer.getServer().getAllLevels().forEach((ws) -> ws.spigotConfig.itemMerge = radius);
+        for (World world : Bukkit.getWorlds()) {
+            ((CraftWorld) world).getHandle().spigotConfig.itemMerge = radius;
+        }
     }
 
     @SuppressWarnings("deprecation")
     static public double getExpMerge() {
-        return MinecraftServer.getServer().getAllLevels().iterator().next().spigotConfig.expMerge;
+        World world = Bukkit.getWorlds().get(0);
+        return ((CraftWorld) world).getHandle().spigotConfig.expMerge;
     }
 
     @SuppressWarnings("deprecation")
     static public void setExpMerge(double radius) {
-        MinecraftServer.getServer().getAllLevels().forEach((ws) -> ws.spigotConfig.expMerge = radius);
+        for (World world : Bukkit.getWorlds()) {
+            ((CraftWorld) world).getHandle().spigotConfig.expMerge = radius;
+        }
     }
 
 }