Monster repeller blocks portal spawns

[Spaghetti-OberNub]

Summary

Added a static instance for GTSpawnEventHandler, as well as an isAreaProtected-method to check if mobs should spawn in a portal. The condition is tested in a mixin.

This is the first time writing a mixin so please take a short look at it when reviewing. :)

Closes Issue 26004

Checklist

• I have tested this PR in DevEnv*
• I have tested this PR in Fullpack
• This PR is in compliance with the GTNH AI Policy

* tested by forcing 20 portal update ticks per tick (see comment)

[Spaghetti-OberNub]

Just FYI, this was used to test spawning if someone else wants to verify or play around with it. (Warning dirty vibe code)

// in GTProxy.java
FMLCommonHandler.instance().bus().register(new SpeedupTickHandler());

// in SpeedupTickHandler.java
package gregtech; 

import cpw.mods.fml.common.eventhandler.SubscribeEvent;
import cpw.mods.fml.common.gameevent.TickEvent;
import net.minecraft.block.BlockPortal;
import net.minecraft.world.WorldServer;
import net.minecraft.world.chunk.Chunk;

public class SpeedupTickHandler {

    private int debugTimer = 0;

    @SubscribeEvent
    public void onWorldTick(TickEvent.WorldTickEvent event) {
        if (event.phase == TickEvent.Phase.START && !event.world.isRemote) {
            WorldServer world = (WorldServer) event.world;

            debugTimer++;
            if (debugTimer >= 20) {
                debugTimer = 0;
            }
            
            for (Object chunkObj : world.theChunkProviderServer.loadedChunks) {
                Chunk chunk = (Chunk) chunkObj;
                
                for (int x = 0; x < 16; x++) {
                    for (int z = 0; z < 16; z++) {
                        for (int y = 0; y < 256; y++) {
                            int realX = chunk.xPosition * 16 + x;
                            int realZ = chunk.zPosition * 16 + z;
                            
                            if (world.getBlock(realX, y, realZ) instanceof BlockPortal) {
                                BlockPortal portal = (BlockPortal) world.getBlock(realX, y, realZ);
                                
                                for (int i = 0; i < 20; i++) {
                                    portal.updateTick(world, realX, y, realZ, world.rand);
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}