Claude review: rust: faux: Allow retrieving a bound Device

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

Patch Review

**Correct and well-justified change.** The `AsRef<device::Device>` → `AsRef<device::Device<device::Bound>>` change strengthens the type-level guarantee.

**Safety comment is thorough:**
```rust
// - faux_match() always returns 1, and probe runs synchronously (PROBE_FORCE_SYNCHRONOUS).
// - suppress_bind_attrs = true on faux_driver prevents userspace-triggered unbind via sysfs
// - mem::forget(Registration) is not a problem; if the Registration is leaked, the faux
//   device stays bound forever.
```
This is exactly the level of reasoning needed. The three points cover the key attack vectors against the `Bound` invariant.

**Potential downstream breakage:** Any existing code using `faux::Registration::as_ref()` where a `&device::Device` (without the `Bound` parameter) was expected will break. Since this is on drm-rust-next and the faux bindings are relatively new, this should be fine, but the cover letter doesn't mention this API change explicitly.

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