Random cleanups to users of Level.OVERWORLD and reduce minecraft_server usage (#1697)

- Use `overworld()` instead of `getLevel(Level.OVERWORLD)` when convenient
- Remove now unnecessary `// OW` comments, from when it had no mappings
- Make spawn chunk size and light batches not depend on global server instance
- Merge all spawn chunk size logic into SpawnChunks instead of methods in the validator
- Remove unneeded `withWorld(OVERWORLD)` with just-created server `CommandSource`s
- Use enhanced for in light batch application

src/main/java/carpet/utils/SpawnChunks.java

@@ -1,15 +1,21 @@
 package carpet.utils;
 
 import carpet.fakes.ChunkTicketManagerInterface;
+import net.minecraft.core.BlockPos;
 import net.minecraft.server.level.DistanceManager;
-import net.minecraft.server.level.ServerChunkCache;
+import net.minecraft.server.level.ServerLevel;
 import net.minecraft.world.level.ChunkPos;
 
 public class SpawnChunks
 {
-    public static void changeSpawnChunks(ServerChunkCache chunkManager, ChunkPos pos, int size)
+    public static void changeSpawnSize(ServerLevel overworld, int size)
     {
-        DistanceManager ticketManager = chunkManager.chunkMap.getDistanceManager();
-        ((ChunkTicketManagerInterface)ticketManager).changeSpawnChunks(pos, size);
+        ChunkPos centerChunk = new ChunkPos(new BlockPos(
+                overworld.getLevelData().getXSpawn(),
+                overworld.getLevelData().getYSpawn(),
+                overworld.getLevelData().getZSpawn()
+        ));
+        DistanceManager ticketManager = overworld.getChunkSource().chunkMap.getDistanceManager();
+        ((ChunkTicketManagerInterface)ticketManager).changeSpawnChunks(centerChunk, size);
     }
 }