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/script/CarpetEventServer.java

@@ -447,9 +447,7 @@ public class CarpetEventServer
             @Override
             public void onTick(MinecraftServer server)
             {
-                handler.call(Collections::emptyList, () ->
-                        server.createCommandSourceStack().withLevel(server.getLevel(Level.OVERWORLD))
-                );
+                handler.call(Collections::emptyList, server::createCommandSourceStack);
             }
         };
 
@@ -458,9 +456,7 @@ public class CarpetEventServer
             @Override
             public void onTick(MinecraftServer server)
             {
-                handler.call(Collections::emptyList, () ->
-                        server.createCommandSourceStack().withLevel(server.getLevel(Level.OVERWORLD))
-                );
+            handler.call(Collections::emptyList,server::createCommandSourceStack);
             }
         };
 
@@ -469,9 +465,7 @@ public class CarpetEventServer
             @Override
             public void onTick(MinecraftServer server)
             {
-                handler.call(Collections::emptyList, () ->
-                        server.createCommandSourceStack().withLevel(server.getLevel(Level.OVERWORLD))
-                );
+            handler.call(Collections::emptyList,server::createCommandSourceStack);
             }
         };
         public static final Event NETHER_TICK = new Event("tick_nether", 0, true)