add block size to the header of a PersistentMap and optimize storage

usage for monotonically incrementing keys.

data-store/src/main/java/org/lucares/pdb/datastore/internal/TagsEncoderDecoder.java

@@ -3,7 +3,7 @@ package org.lucares.pdb.datastore.internal;
 import org.lucares.pdb.api.Tags;
 import org.lucares.pdb.map.PersistentMap.EncoderDecoder;
 
-class TagsEncoderDecoder implements EncoderDecoder<Tags> {
+public class TagsEncoderDecoder implements EncoderDecoder<Tags> {
     @Override
     public byte[] encode(final Tags tags) {
         return tags.toBytes();