[style] format crate import style:

```rust
mod sub_mod1;
mod sub_mod2;

use core::foo::Bar;
use alloc::bar::Foo;

use ext_crate::bar;

use crate::baz;
use self::sub_mod1::foo;
use super::sup_mod::qux;

pub use ...
```

src/loader.rs

@@ -3,9 +3,9 @@
 //! It will read and parse ELF files.
 //!
 //! Now these apps are loaded into memory as a part of the kernel image.
+use alloc::{collections::btree_map::BTreeMap, vec::Vec};
 use core::arch::global_asm;
 
-use alloc::{collections::btree_map::BTreeMap, vec::Vec};
 use axhal::paging::MappingFlags;
 use memory_addr::{MemoryAddr, VirtAddr};
 

src/main.rs

@@ -12,6 +12,7 @@ mod loader;
 mod mm;
 mod syscall_imp;
 mod task;
+
 use alloc::sync::Arc;
 
 use axhal::arch::UspaceContext;

src/mm.rs

@@ -1,14 +1,13 @@
 use alloc::string::ToString;
-use axerrno::AxResult;
-use memory_addr::VirtAddr;
 
+use axerrno::AxResult;
 use axhal::{
     paging::MappingFlags,
     trap::{register_trap_handler, PAGE_FAULT},
 };
-
 use axmm::AddrSpace;
 use axtask::TaskExtRef;
+use memory_addr::VirtAddr;
 
 use crate::{config, loader};
 

src/syscall_imp/task/mod.rs

@@ -1,4 +1,5 @@
 mod schedule;
 mod thread;
+
 pub(crate) use self::schedule::*;
 pub(crate) use self::thread::*;

src/syscall_imp/task/thread.rs

@@ -1,5 +1,4 @@
 use arceos_posix_api::{self as api};
-
 use axtask::{current, TaskExtRef};
 use num_enum::TryFromPrimitive;
 

src/task.rs

@@ -1,6 +1,5 @@
-use core::sync::atomic::AtomicU64;
-
 use alloc::sync::Arc;
+use core::sync::atomic::AtomicU64;
 
 use axhal::arch::UspaceContext;
 use axmm::AddrSpace;