Hide subterrain gate accessors

- The memoized subterrain dimension gate no longer gets generated getter and setter methods

core/src/main/java/art/arcane/iris/generation/runtime/IrisEngine.java

@@ -179,6 +179,8 @@ public class IrisEngine implements Engine {
     @Getter(AccessLevel.NONE)
     @Setter(AccessLevel.NONE)
     private volatile boolean generationHistoryRoutingRequired;
+    @Getter(AccessLevel.NONE)
+    @Setter(AccessLevel.NONE)
     private volatile SubterrainGate subterrainGate;
     @Getter(AccessLevel.NONE)
     @Setter(AccessLevel.NONE)