added WIP 'custom_dimension' to the API

src/main/java/carpet/mixins/MinecraftServer_scarpetMixin.java

@@ -4,8 +4,11 @@ import carpet.CarpetServer;
 import carpet.fakes.MinecraftServerInterface;
 import net.minecraft.server.MinecraftServer;
 import net.minecraft.server.ServerTask;
+import net.minecraft.server.world.ServerWorld;
 import net.minecraft.util.Util;
+import net.minecraft.util.registry.RegistryKey;
 import net.minecraft.util.thread.ReentrantThreadExecutor;
+import net.minecraft.world.World;
 import net.minecraft.world.level.storage.LevelStorage;
 import org.spongepowered.asm.mixin.Final;
 import org.spongepowered.asm.mixin.Mixin;
@@ -14,6 +17,7 @@ import org.spongepowered.asm.mixin.injection.At;
 import org.spongepowered.asm.mixin.injection.Inject;
 import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
 
+import java.util.Map;
 import java.util.function.BooleanSupplier;
 
 import static carpet.script.CarpetEventServer.Event.ENDER_TICK;
@@ -38,6 +42,8 @@ public abstract class MinecraftServer_scarpetMixin extends ReentrantThreadExecut
 
     @Shadow @Final protected LevelStorage.Session session;
 
+    @Shadow @Final private Map<RegistryKey<World>, ServerWorld> worlds;
+
     @Override
     public void forceTick(BooleanSupplier isAhead)
     {
@@ -52,6 +58,12 @@ public abstract class MinecraftServer_scarpetMixin extends ReentrantThreadExecut
         return session;
     }
 
+    @Override
+    public Map<RegistryKey<World>, ServerWorld> getCMWorlds()
+    {
+        return worlds;
+    }
+
     @Inject(method = "tick", at = @At(
             value = "CONSTANT",
             args = "stringValue=tallying"