Fix ConcurrentModificationException in NewChunksHack

[Theoreb]

Description

Fix ConcurrentModificationException in NewChunksHack by iterating over copies of newChunks and oldChunks during buffer update. This prevents crashes when these sets are modified from other threads.

Description: Firing Wurst event

java.util.ConcurrentModificationException at java.base/java.util.HashMap$HashIterator.nextNode(HashMap.java:1605) at java.base/java.util.HashMap$KeyIterator.next(HashMap.java:1628) at knot//net.wurstclient.hacks.newchunks.NewChunksOutlineRenderer.buildBuffer(NewChunksOutlineRenderer.java:29) at knot//net.wurstclient.hacks.NewChunksHack.lambda$onUpdate$2(NewChunksHack.java:172) at knot//net.wurstclient.util.EasyVertexBuffer.createAndUpload(EasyVertexBuffer.java:45) at knot//net.wurstclient.util.BufferWithLayer.createAndUpload(BufferWithLayer.java:22) at knot//net.wurstclient.hacks.newchunks.NewChunksRenderer.updateBuffer(NewChunksRenderer.java:43) at knot//net.wurstclient.hacks.NewChunksHack.onUpdate(NewChunksHack.java:171) at knot//net.wurstclient.events.UpdateListener$UpdateEvent.fire(UpdateListener.java:27) at knot//net.wurstclient.event.EventManager.fireImpl(EventManager.java:69) at knot//net.wurstclient.event.EventManager.fire(EventManager.java:42) at knot//net.minecraft.class_746.handler$blh001$wurst$onTick(class_746.java:1880) at knot//net.minecraft.class_746.method_5773(class_746.java:221) at knot//net.minecraft.class_1297.method_5842(class_1297.java:2154) at knot//net.minecraft.class_1309.method_5842(class_1309.java:2971) at knot//net.minecraft.class_1657.method_5842(class_1657.java:560) at knot//net.minecraft.class_746.method_5842(class_746.java:901) at knot//net.minecraft.class_638.method_18647(class_638.java:299) at knot//net.minecraft.class_638.method_18646(class_638.java:282) at knot//net.minecraft.class_1937.method_18472(class_1937.java:498) at knot//net.minecraft.class_638.method_32124(class_638.java:261) at knot//net.minecraft.class_5574.method_31791(class_5574.java:54) at knot//net.minecraft.class_638.method_18116(class_638.java:257) at knot//net.minecraft.class_310.method_1574(class_310.java:1956) at knot//net.minecraft.class_310.method_1523(class_310.java:1246) at knot//net.minecraft.class_310.method_1514(class_310.java:882) at knot//net.minecraft.client.main.Main.main(Main.java:256) at net.fabricmc.loader.impl.game.minecraft.MinecraftGameProvider.launch(MinecraftGameProvider.java:480) at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:74) at net.fabricmc.loader.impl.launch.knot.KnotClient.main(KnotClient.java:23)

[CLAassistant]

All committers have signed the CLA.

[Theoreb]

The problem only arises when using certain optimisation or rendering modification mods. This fix is therefore not always necessary, but it can be useful for ensuring compatibility.