rust: alloc: cleanup doctest imports to "kernel vertical" style

Change all imports in the alloc module's doctests to use the "kernel
vertical" import style [1].

While at it, drop imports that are automatically included in doctests.

Link: https://docs.kernel.org/rust/coding-guidelines.html#imports [1]
Reviewed-by: Eliot Courtney <ecourtney@nvidia.com>
Link: https://patch.msgid.link/20260513190946.619810-2-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

rust/kernel/alloc/allocator.rs

@@ -174,8 +174,11 @@ impl Vmalloc {
     /// # Examples
     ///
     /// ```
-    /// # use core::ptr::{NonNull, from_mut};
-    /// # use kernel::{page, prelude::*};
+    /// # use core::ptr::{
+    /// #     from_mut,
+    /// #     NonNull, //
+    /// # };
+    /// # use kernel::page;
     /// use kernel::alloc::allocator::Vmalloc;
     ///
     /// let mut vbox = VBox::<[u8; page::PAGE_SIZE]>::new_uninit(GFP_KERNEL)?;

rust/kernel/alloc/kbox.rs

@@ -297,7 +297,10 @@ pub fn pin(x: T, flags: Flags) -> Result<Pin<Box<T, A>>, AllocError>
     /// # Examples
     ///
     /// ```
-    /// use kernel::sync::{new_spinlock, SpinLock};
+    /// use kernel::sync::{
+    ///     new_spinlock,
+    ///     SpinLock, //
+    /// };
     ///
     /// struct Inner {
     ///     a: u32,
@@ -590,7 +593,6 @@ fn deref_mut(&mut self) -> &mut T {
 ///
 /// ```
 /// # use core::borrow::Borrow;
-/// # use kernel::alloc::KBox;
 /// struct Foo<B: Borrow<u32>>(B);
 ///
 /// // Owned instance.
@@ -618,7 +620,6 @@ fn borrow(&self) -> &T {
 ///
 /// ```
 /// # use core::borrow::BorrowMut;
-/// # use kernel::alloc::KBox;
 /// struct Foo<B: BorrowMut<u32>>(B);
 ///
 /// // Owned instance.
@@ -683,9 +684,13 @@ fn drop(&mut self) {
 /// # Examples
 ///
 /// ```
-/// # use kernel::prelude::*;
-/// use kernel::alloc::allocator::VmallocPageIter;
-/// use kernel::page::{AsPageIter, PAGE_SIZE};
+/// use kernel::{
+///     alloc::allocator::VmallocPageIter,
+///     page::{
+///         AsPageIter,
+///         PAGE_SIZE, //
+///     }, //
+/// };
 ///
 /// let mut vbox = VBox::new((), GFP_KERNEL)?;
 ///

rust/kernel/alloc/kvec.rs

@@ -1187,9 +1187,13 @@ fn into_iter(self) -> Self::IntoIter {
 /// # Examples
 ///
 /// ```
-/// # use kernel::prelude::*;
-/// use kernel::alloc::allocator::VmallocPageIter;
-/// use kernel::page::{AsPageIter, PAGE_SIZE};
+/// use kernel::{
+///     alloc::allocator::VmallocPageIter,
+///     page::{
+///         AsPageIter,
+///         PAGE_SIZE, //
+///     }, //
+/// };
 ///
 /// let mut vec = VVec::<u8>::new();
 ///

rust/kernel/alloc/layout.rs

@@ -50,7 +50,10 @@ pub const fn empty() -> Self {
     /// # Examples
     ///
     /// ```
-    /// # use kernel::alloc::layout::{ArrayLayout, LayoutError};
+    /// # use kernel::alloc::layout::{
+    /// #     ArrayLayout,
+    /// #     LayoutError, //
+    /// # };
     /// let layout = ArrayLayout::<i32>::new(15)?;
     /// assert_eq!(layout.len(), 15);
     ///