refactor(host_network): extract NetworkManager as a reusable component

examples/nanodc/src/main.rs

@@ -1,6 +1,6 @@
 use std::{
     net::{IpAddr, Ipv4Addr},
-    sync::Arc,
+    sync::{Arc, OnceLock},
 };
 
 use brocade::BrocadeOptions;
@@ -107,6 +107,7 @@ async fn main() {
             },
         ],
         switch_client: switch_client.clone(),
+        network_manager: OnceLock::new(),
     };
 
     let inventory = Inventory {