rust: kernel: move `ARef<T>` and `AlwaysRefCounted` to new `sync::aref` module

Refactor the `ARef` type and `AlwaysRefCounted` trait from `types.rs`
into a new `sync/aref.rs` module:

 - Add `rust/kernel/sync/aref.rs` with the definitions of `ARef` and
   `AlwaysRefCounted`.

 - Remove the same type and trait definitions from `rust/kernel/types.rs`.

 - Update relevant files to import `ARef` and `AlwaysRefCounted` from
   `sync/aref.rs`.

The type and trait definitions remain unchanged.

Suggested-by: Benno Lossin <benno.lossin@proton.me>
Link: https://github.com/Rust-for-Linux/linux/issues/1117
Signed-off-by: Aliet Exposito Garcia <aliet.exposito@gmail.com>
Reviewed-by: Fiona Behrens <me@kloenk.dev>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20240918225115.2309224-3-aliet.exposito@gmail.com
[ Rebased on top of the lints series, slightly reworded and removed
  unneeded `use AlwaysRefCounted` in example. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
index 55dff7e088bf..0b358aceace6 100644
--- a/rust/kernel/task.rs
+++ b/rust/kernel/task.rs
@@ -61,7 +61,7 @@ macro_rules! current {
 /// incremented when creating `State` and decremented when it is dropped:
 ///
 /// ```
-/// use kernel::{task::Task, types::ARef};
+/// use kernel::{task::Task, sync::aref::ARef};
 ///
 /// struct State {
 ///     creator: ARef<Task>,
@@ -164,7 +164,7 @@ impl Task {
 }
 
 // SAFETY: The type invariants guarantee that `Task` is always refcounted.
-unsafe impl crate::types::AlwaysRefCounted for Task {
+unsafe impl crate::sync::aref::AlwaysRefCounted for Task {
     fn inc_ref(&self) {
         // SAFETY: The existence of a shared reference means that the refcount is nonzero.
         unsafe { bindings::get_task_struct(self.0.get()) };