build: fix dead_code warnings without "app" feature

src/sysinfo_snapshot.rs

@@ -13,6 +13,7 @@ pub struct SysinfoSnapshot {
     pub swap_total: u64,
 }
 impl SysinfoSnapshot {
+    #[cfg_attr(not(feature = "app"), allow(dead_code))]
     pub fn uptime(&self) -> Duration {
         Duration::from_secs(self.uptime)
     }

src/utils.rs

@@ -1,3 +1,4 @@
+#[cfg_attr(not(feature = "app"), allow(dead_code))]
 pub trait Toggle {
     fn toggle(&mut self);
 }