feat: Add comment & delete unused file & improve user command processing logic

Walkthrough

此次更改主要集中在 pikiwidb 应用程序的命令行工具上，改善了命令行参数解析、文档、版权信息，并提升了代码注释的清晰度。引入了多个新命令行选项，规范了代码结构，使得用户体验更加友好。

Changes

文件	更改摘要
`README.md`	修改了命令行使用的配置文件路径，增强了可读性和一致性。
`src/base_cmd.cc`	更新了文件头部注释，添加了文件功能描述并更新了版权声明。
`src/cmd_thread_pool.h`	增强了文档说明，统一了方法注释格式，明确了线程池的功能。
`src/config.h`	添加了详细的文档，更新了方法和数据成员的注释，扩展了配置功能。
`src/pikiwidb.cc`	改进了命令行参数解析，更新了 `main` 函数签名以符合 C++ 习惯，添加了新命令行选项。

Sequence Diagram(s)

sequenceDiagram
    participant User
    participant PikiwiDB
    User->>PikiwiDB: 输入命令行参数
    PikiwiDB->>PikiwiDB: 解析参数
    alt 使用配置文件
        PikiwiDB->>PikiwiDB: 读取配置文件
    end
    PikiwiDB->>User: 启动并显示状态

兔兔舞动欢喜舞，
新增功能真奇妙，
配置文件轻松选，
版权更新不再愁。
代码清晰如晨光，
PikiwiDB更辉煌！
🐰✨

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OpenAtomFoundation / pikiwidb