fix(cluster): gate readiness warn import to Linux

The `warn` import in readiness.rs is only used by the Linux systemd
notification path. On non-Linux targets that path is compiled out, leaving
the import unused and breaking `clippy -D warnings`. Gate the import to
target_os = "linux" so non-Linux builds lint cleanly.

Author: farhan-syah

nodedb-cluster/src/readiness.rs

@@ -13,7 +13,9 @@
 //! no-op so the server builds and runs unchanged; `sd-notify` itself
 //! is only compiled in on Linux via a target-gated Cargo dependency.
 
-use tracing::{debug, warn};
+use tracing::debug;
+#[cfg(target_os = "linux")]
+use tracing::warn;
 
 /// Signal that the server is fully initialised.
 ///