Function normalize_dir 

pub fn normalize_dir(v: &str) -> String

Modified from the opendal::raw::normalize_root

The different

It doesn’t always append / ahead of the path, It only keeps / ahead if the original path starts with /.

Make sure the directory is normalized to style like abc/def/.

Normalize Rules

• All whitespace will be trimmed: abc/def => abc/def
• All leading / will be trimmed: ///abc => abc
• Internal // will be replaced by /: abc///def => abc/def
• Empty path will be /: `` => /
• (Removed❗️) Add leading / if not starts with: abc/ => /abc/
• Add trailing / if not ends with: /abc => /abc/

Finally, we will got path like /path/to/root/.