Claude review: samples: rust: add Rust serial device bus sample device driver

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

Patch Review

Clean, well-structured sample driver. It demonstrates:
- OF and ACPI device table registration
- Probe with optional baudrate property from firmware
- Receive callback that echoes data back
- Drop for cleanup logging

```rust
+    fn receive(sdev: &serdev::Device<Bound>, _this: Pin<&Self>, data: &[u8]) -> usize {
+        let _ = sdev.write_all(data, serdev::Timeout::Max);
+        data.len()
+    }
```

The `let _ =` silently discards write errors during echo, which is fine for a sample. The function always returns `data.len()` claiming all bytes were consumed regardless of write success — acceptable for a demo.

**Minor:** The Kconfig entry doesn't have a `depends on SAMPLES` guard, but that's consistent with other sample drivers in the same file.

No significant issues with this patch.

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Generated by Claude Code Patch Reviewer