Add PersistenceService interface for region persistence operations

src/main/java/com/livingworld/core/services/PersistenceService.java

@@ -0,0 +1,50 @@
+package com.livingworld.core.services;
+
+import com.livingworld.regions.Region;
+import com.livingworld.regions.RegionCoordinate;
+
+import java.util.Optional;
+
+/**
+ * Service interface for region persistence operations.
+ *
+ * <p>This service handles marking regions as dirty, saving and loading regions,
+ * and flushing all pending changes to storage.</p>
+ */
+public interface PersistenceService {
+
+    /**
+     * Marks a region as dirty, indicating it has unsaved changes.
+     *
+     * @param region the region to mark as dirty (must not be null)
+     * @throws IllegalArgumentException if region is null
+     */
+    void markRegionDirty(Region region);
+
+    /**
+     * Saves all regions that have been marked as dirty.
+     */
+    void saveDirtyRegions();
+
+    /**
+     * Loads a region from storage by its coordinate.
+     *
+     * @param coordinate the region coordinate (must not be null)
+     * @return an Optional containing the loaded region if it exists, or empty if not found
+     * @throws IllegalArgumentException if coordinate is null
+     */
+    Optional<Region> loadRegion(RegionCoordinate coordinate);
+
+    /**
+     * Saves a region to storage.
+     *
+     * @param region the region to save (must not be null)
+     * @throws IllegalArgumentException if region is null
+     */
+    void saveRegion(Region region);
+
+    /**
+     * Flushes all pending changes to storage, ensuring data integrity.
+     */
+    void flushAll();
+}