rust: alloc: implement Borrow and BorrowMut for Vec

Implement `Borrow<[T]>` and `BorrowMut<[T]>` for `Vec<T>`. This allows
`Vec<T>` to be used in generic APIs asking for types implementing those
traits. `[T; N]` and `&mut [T]` also implement those traits allowing
users to use either owned, borrowed and heap-owned values.

The implementation leverages `as_slice` and `as_mut_slice`.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://lore.kernel.org/r/20250616-borrow_impls-v4-1-36f9beb3fe6a@nvidia.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

rust/kernel/alloc/kvec.rs

@@ -8,6 +8,7 @@ use super::{
     AllocError, Allocator, Box, Flags,
 };
 use core::{
+    borrow::{Borrow, BorrowMut},
     fmt,
     marker::PhantomData,
     mem::{ManuallyDrop, MaybeUninit},
@@ -890,6 +891,58 @@ where
     }
 }
 
+/// # Examples
+///
+/// ```
+/// # use core::borrow::Borrow;
+/// struct Foo<B: Borrow<[u32]>>(B);
+///
+/// // Owned array.
+/// let owned_array = Foo([1, 2, 3]);
+///
+/// // Owned vector.
+/// let owned_vec = Foo(KVec::from_elem(0, 3, GFP_KERNEL)?);
+///
+/// let arr = [1, 2, 3];
+/// // Borrowed slice from `arr`.
+/// let borrowed_slice = Foo(&arr[..]);
+/// # Ok::<(), Error>(())
+/// ```
+impl<T, A> Borrow<[T]> for Vec<T, A>
+where
+    A: Allocator,
+{
+    fn borrow(&self) -> &[T] {
+        self.as_slice()
+    }
+}
+
+/// # Examples
+///
+/// ```
+/// # use core::borrow::BorrowMut;
+/// struct Foo<B: BorrowMut<[u32]>>(B);
+///
+/// // Owned array.
+/// let owned_array = Foo([1, 2, 3]);
+///
+/// // Owned vector.
+/// let owned_vec = Foo(KVec::from_elem(0, 3, GFP_KERNEL)?);
+///
+/// let mut arr = [1, 2, 3];
+/// // Borrowed slice from `arr`.
+/// let borrowed_slice = Foo(&mut arr[..]);
+/// # Ok::<(), Error>(())
+/// ```
+impl<T, A> BorrowMut<[T]> for Vec<T, A>
+where
+    A: Allocator,
+{
+    fn borrow_mut(&mut self) -> &mut [T] {
+        self.as_mut_slice()
+    }
+}
+
 impl<T: Eq, A> Eq for Vec<T, A> where A: Allocator {}
 
 impl<T, I: SliceIndex<[T]>, A> Index<I> for Vec<T, A>