Claude review: rust: device: generalize drvdata methods over ForLt

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

Patch Review

This is the critical patch that changes how driver private data is stored/retrieved.

In `set_drvdata`:
```rust
pub fn set_drvdata<'bound, F: ForLt>(
    &self,
    data: impl PinInit<F::Of<'bound>, Error>,
) -> Result {
    let data = KBox::pin_init(data, GFP_KERNEL)?;
    let ptr = KBox::into_raw(unsafe { Pin::into_inner_unchecked(data) });
    unsafe { bindings::dev_set_drvdata(self.as_raw(), ptr.cast()) };
    Ok(())
}
```

The key insight is that `F::Of<'bound>` and `F::Of<'static>` have identical layout (lifetimes are erased at runtime), so storing via raw pointer is sound. The `Pin::into_inner_unchecked` is safe because we're immediately converting to a raw pointer.

In `drvdata_unchecked`:
```rust
let pinned: Pin<&F::Of<'static>> =
    unsafe { Pin::<KBox<F::Of<'static>>>::borrow(ptr.cast()) };
unsafe { Pin::new_unchecked(F::cast_ref(pinned.get_ref())) }
```

This reconstructs a `Pin<&F::Of<'_>>` by first borrowing as `'static`, then shortening the lifetime via `ForLt::cast_ref`. The `Pin::new_unchecked` is justified because the data was pinned when stored and lifetime shortening doesn't affect pinning.

**Minor:** The transition from `ForeignOwnable`-based storage (`into_foreign`/`from_foreign`/`borrow`) to raw `KBox::into_raw`/`KBox::from_raw` changes the abstraction level. This is fine but means the `ForeignOwnable` import for `Pin<KBox<T>>` is likely now unused. The diff doesn't show whether that import is cleaned up.

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Generated by Claude Code Patch Reviewer