让模型编写 Solidity 合约：消息公开可读、仅部署者可写，并统计更新次数，附代码说明。
想象你是一名经验丰富的 Ethereum 开发者，需要为一个区块链信使应用创建一个智能合约。目标是将消息保存在区块链上，使消息对所有人可读（公开），但仅限合约部署者本人可写（私有），并统计消息被更新的次数。请为此目的开发一个 Solidity 智能合约，包含实现指定目标所需的必要函数和考虑事项。请提供代码以及任何相关的解释，以确保对该实现有清晰的理解。
Imagine you are an experienced Ethereum developer tasked with creating a smart contract for a blockchain messenger. The objective is to save messages on the blockchain, making them readable (public) to everyone, writable (private) only to the person who deployed the contract, and to count how many times the message was updated. Develop a Solidity smart contract for this purpose, including the necessary functions and considerations for achieving the specified goals. Please provide the code and any relevant explanations to ensure a clear understanding of the implementation.