docs: def get_lastblock(cls, impl, working_dir):
          """
          What was the last block processed?
          Return the number on success
          Return None on failure to read
          """
          if not cls.db_exists(impl, working_dir):
              return None
  
          con = cls.db_open(impl, working_dir)
          query = 'SELECT MAX(block_id) FROM snapshots;'
          
          rows = cls.db_query_execute(con, query, (), verbose=False)
          ret = None
          for r in rows:
              ret = r['MAX(block_id)']
  
          con.close()
          return ret