code: func WriteFastTrieProgress(db ethdb.Writer, count uint64) {
  	if err := db.Put(fastTrieProgressKey, new(big.Int).SetUint64(count).Bytes()); err != nil {
  		log.Crit("Failed to store fast sync trie progress", "err", err)
  	}
  }
docs: // WriteFastTrieProgress stores the fast sync trie process counter to support
  // retrieving it across restarts.