Refactor MerkleTree to prevent flushing to disk when there are no unsaved changes for improved resource management

Author: EAOE3

src/main/java/io/pwrlabs/database/rocksdb/MerkleTree.java

@@ -375,6 +375,8 @@ public BiResult<List<byte[]>, List<byte[]>> keysAndTheirValues() {
      * Flush all in-memory changes (nodes, metadata) to RocksDB.
      */
     public void flushToDisk() throws RocksDBException {
+        if(!hasUnsavedChanges.get()) return;
+
         long startTime = System.currentTimeMillis();
         errorIfClosed();
         getWriteLock();