用户访问/下载统计

### Please make sure of the following things

- [x] I have read the [documentation](https://alistgo.com).
- [x] I'm sure there are no duplicate issues or discussions.
- [x] I'm sure this feature is not implemented.
- [x] I'm sure it's a reasonable and popular requirement.

### Description of the feature / 需求描述

- 为每个用户记录：
- **访问量**（visits）
- **下载量**（downloads）
- 数据存储：文件 `{DataDir}/stat/users.json`
- 管理端接口：
- 查询用户访问量、下载量
- 支持单用户或列表查询

### Suggested solution / 实现思路

_No response_

### Additional context / 附件

_No response_