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

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

Patch Review

Clean and functional sample driver. A few observations:

**Echoing data in receive callback:**
```rust
+    fn receive(sdev: &serdev::Device<Bound>, _this: Pin<&Self>, data: &[u8]) -> usize {
+        let _ = sdev.write_all(data, serdev::Timeout::Max);
+        data.len()
+    }
```
The `write_all` with `Timeout::Max` could block indefinitely if the device can't accept data. For a sample this is acceptable, but a brief comment noting this is intentional would be helpful. Also, `let _ =` silently discards write errors, which is fine for a sample.

**Baudrate handling:**
```rust
+        if sdev
+            .set_baudrate(
+                dev.fwnode()
+                    .and_then(|fwnode| fwnode.property_read(c"baudrate").optional())
+                    .unwrap_or(115200),
+            )
+            .is_err()
+        {
+            return Err(EINVAL);
+        }
```
Reading a `baudrate` property from firmware and falling back to 115200 is a reasonable pattern. The `set_baudrate` error (which contains the actual baudrate set) is discarded and replaced with `EINVAL`, which is appropriate.

**Kconfig entry properly uses `select`:**
```
+	select RUST_SERIAL_DEV_BUS_ABSTRACTIONS
```
This ensures the abstraction is compiled when the sample is enabled. Correct.

The sample effectively demonstrates OF and ACPI device table setup, probe/remove lifecycle, baudrate/flow-control/parity configuration, and the receive callback -- good coverage for a sample driver.

---
Generated by Claude Code Patch Reviewer