Claude review: rust: Add `OwnableRefCounted`

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

This adds the `OwnableRefCounted` trait for converting between `Owned<T>` and `ARef<T>`.

> +    /// Converts the [`Owned`] into an [`ARef`].
> +    fn into_shared(this: Owned<Self>) -> ARef<Self> {
> +        // SAFETY: Safe by the requirements on implementing the trait.
> +        unsafe { ARef::from_raw(Owned::into_raw(this)) }
> +    }

The safety comment here is vague. `OwnableRefCounted` is a safe trait (not `unsafe trait`), so "requirements on implementing the trait" isn't well-defined. The actual safety depends on: (1) `Ownable::release` effectively performing a `dec_ref` (so the `Owned` corresponds to a ref count increment), and (2) whoever created the `Owned` having established that ref count correctly. This chain of reasoning should be documented more explicitly, either in the safety comment or in the trait-level documentation as a prerequisite for implementers.

There is also a documentation link error in the change to `aref.rs`:

> +/// [`OwnableRefCounted`] allows to convert between unique and
> +/// shared references (i.e. [`Owned<Self>`](crate::types::Owned) and
> +/// [`ARef<Self>`](crate::types::Owned)).

The link target for `ARef<Self>` is `crate::types::Owned`, which is wrong. It should link to `ARef`, not `Owned`.

The `TryFrom<ARef<T>> for Owned<T>` and `From<Owned<T>> for ARef<T>` implementations look correct and follow standard Rust conversion patterns.

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