Add TUN interface with async netlink configuration

- Implement fips.rs binary with config loading, node creation, and logging
- Create src/tun.rs module (TunDevice, TunState, TunError)
- Use rtnetlink crate for IPv6 address configuration
- Make TunDevice::create() and Node::init_tun() async
- Add IPv6 disabled check with helpful error message
- Add rtnetlink, tokio, futures dependencies
- Single tokio current_thread runtime for entire driver

162 tests pass.

Cargo.toml

@@ -13,6 +13,12 @@ serde = { version = "1.0", features = ["derive"] }
 serde_yaml = "0.9"
 dirs = "6.0"
 hex = "0.4"
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+tun = { version = "0.7", features = ["async"] }
+rtnetlink = "0.14"
+tokio = { version = "1", features = ["rt", "macros"] }
+futures = "0.3"
 
 [dev-dependencies]
 tempfile = "3.15"