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>

virtio-devices/src/lib.rs

@@ -39,7 +39,8 @@ pub mod vhost_user;
 pub mod vsock;
 pub mod watchdog;
 
-use vm_memory::{bitmap::AtomicBitmap, GuestAddress, GuestMemory};
+use vm_memory::bitmap::AtomicBitmap;
+use vm_memory::{GuestAddress, GuestMemory};
 use vm_virtio::VirtioDeviceType;
 
 pub use self::balloon::Balloon;