Throw when sync loading chunks after shutdown

The caller would block indefinitely if a sync load is requested
during shutdown. Rather than block indefinitely, we should throw
an exception to indicate to the caller that the chunk system is
unable to process requests.

src/main/java/ca/spottedleaf/moonrise/mixin/chunk_system/ServerChunkCacheMixin.java

@@ -86,6 +86,13 @@ private ChunkAccess syncLoad(final int chunkX, final int chunkZ, final ChunkStat
                 completable::complete
         );
 
+        if (!completable.isDone() && chunkTaskScheduler.hasShutdown()) {
+            throw new IllegalStateException(
+                "Chunk system has shut down, cannot process chunk requests in world '" + ca.spottedleaf.moonrise.common.util.WorldUtil.getWorldName(this.level) + "' at "
+                    + "(" + chunkX + "," + chunkZ + ") status: " + toStatus
+            );
+        }
+
         if (TickThread.isTickThreadFor(this.level, chunkX, chunkZ)) {
             ChunkTaskScheduler.pushChunkWait(this.level, chunkX, chunkZ);
             this.mainThreadProcessor.managedBlock(completable::isDone);

src/main/java/ca/spottedleaf/moonrise/patches/chunk_system/scheduling/ChunkHolderManager.java

@@ -219,6 +219,8 @@ public void close(final boolean save, final boolean halt) {
                 LOGGER.error("Failed to close '" + type.name() + "' regionfile cache for world '" + WorldUtil.getWorldName(this.world) + "'", ex);
             }
         }
+
+        this.taskScheduler.setShutdown(true);
     }
 
     void ensureInAutosave(final NewChunkHolder holder) {

src/main/java/ca/spottedleaf/moonrise/patches/chunk_system/scheduling/ChunkTaskScheduler.java

@@ -271,6 +271,16 @@ public final int getChunkSystemLockShift() {
         return this.lockShift;
     }
 
+    private volatile boolean shutdown;
+
+    public boolean hasShutdown() {
+        return this.shutdown;
+    }
+
+    public void setShutdown(final boolean shutdown) {
+        this.shutdown = shutdown;
+    }
+
     public ChunkTaskScheduler(final ServerLevel world) {
         this.world = world;
         // must be >= region shift (in paper, doesn't exist) and must be >= ticket propagator section shift
@@ -525,6 +535,13 @@ public ChunkAccess syncLoadNonFull(final int chunkX, final int chunkZ, final Chu
             return loaded;
         }
 
+        if (this.hasShutdown()) {
+            throw new IllegalStateException(
+                "Chunk system has shut down, cannot process chunk requests in world '" + ca.spottedleaf.moonrise.common.util.WorldUtil.getWorldName(this.world) + "' at "
+                    + "(" + chunkX + "," + chunkZ + ") status: " + status
+            );
+        }
+
         final Long ticketId = getNextNonFullLoadId();
         final int ticketLevel = getTicketLevel(status);
         this.chunkHolderManager.addTicketAtLevel(NON_FULL_CHUNK_LOAD, chunkX, chunkZ, ticketLevel, ticketId);