misc: Further improve imports styling

By introducing `imports_granularity="Module"` format strategy,
effectively groups imports from the same module into one line or block,
improving maintainability and readability.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>

vmm/src/config.rs

@@ -4,10 +4,9 @@
 //
 
 use std::collections::{BTreeSet, HashMap};
-use std::fmt;
 use std::path::PathBuf;
-use std::result;
 use std::str::FromStr;
+use std::{fmt, result};
 
 use clap::ArgMatches;
 use option_parser::{