通过 readdir(3) 异步地读取下一个目录条目作为 <fs.Dirent>

    Asynchronously read the next directory entry via readdir(3) as an <fs.Dirent>.

    After the read is completed, the callback will be called with an <fs.Dirent>, or null if there are no more directory entries to read.

    Directory entries returned by this function are in no particular order as provided by the operating system's underlying directory mechanisms. Entries added or removed while iterating over the directory might not be included in the iteration results.