perf: async autosave for dedicated server

Autosave previously froze the main thread for 2-6 seconds while
compressing the entire save file with zlib. Now the save buffer is
snapshotted under the lock (~18ms), then compression runs on a
background thread. The compressed data is committed to StorageManager
on the next main-thread tick via CommitPendingAsyncSave().

Also skip redundant full chunk saves during autosave on the dedicated
server -- chunks are already persisted by the per-tick trickle save.
Only entity data is flushed, matching Xbox/Orbis behavior.

Added per-step timing to the autosave handler for diagnostics.

Minecraft.World/ConsoleSaveFileOriginal.h

@@ -77,6 +77,11 @@ public:
 	virtual void LockSaveAccess();
 	virtual void ReleaseSaveAccess();
 
+#ifdef _WINDOWS64
+	// Called from the main thread to commit a completed async save to StorageManager.
+	static void CommitPendingAsyncSave();
+#endif
+
 	virtual ESavePlatform getSavePlatform();
 	virtual bool isSaveEndianDifferent();
 	virtual void setLocalPlatform();