Do not allow chunk unloading outside of the regular tick loop

Allowing chunk loading to occur at any point via purgeUnload()
introduces possible undesirable behavior to occur recursively
inside the chunk system.

patches/server/Moonrise-optimisation-patches.patch

@@ -25504,6 +25504,11 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
      }
  
      // CraftBukkit start - modelled on below
+     public void purgeUnload() {
++        if (true) return; // Paper - rewrite chunk system
+         this.level.getProfiler().push("purge");
+         this.distanceManager.purgeStaleTickets();
+         this.runDistanceManagerUpdates();
 @@ -0,0 +0,0 @@ public class ServerChunkCache extends ChunkSource {
          this.level.getProfiler().popPush("chunks");
          if (tickChunks) {