add option to backup a single device

src/main.rs

@@ -16,6 +16,7 @@ mod config;
 #[derive(Debug, Parser)]
 struct Args {
     config: PathBuf,
+    device: Option<String>,
 }
 
 #[tokio::main]
@@ -35,6 +36,7 @@ async fn main() -> Result<()> {
     let devices = client.current_devices();
     info!("found {} devices", devices.len());
     for device in devices {
+        if args.device.is_none() || args.device.as_deref() == Some(device.as_str()) {
             let result = timeout(
                 Duration::from_secs(120),
                 download(&client, &device, &config.output.target, &device_password),
@@ -47,6 +49,7 @@ async fn main() -> Result<()> {
                 error!(device = device, error = %e, "Failed to download config for {device}");
             }
         }
+    }
 
     Ok(())
 }