fix(agent): gate now binding to logging feature

The Windows CI matrix surfaced an `unused_variables` warning at
metrics.rs:846 — `let now = std::time::Instant::now();` was bound
unconditionally but only consumed inside a `#[cfg(feature = "logging")]`
tracing::debug! call.

This block lives in the non-Linux `collect_processes_all`, so the Linux
CI never compiles it and never sees the warning. Same shape as the
`processes_ttl_ms` Windows fix from earlier: a binding whose only
consumer is cfg-gated needs to be cfg-gated too.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

socktop_agent/src/metrics.rs

@@ -843,6 +843,13 @@ pub async fn collect_processes_all(state: &AppState) -> ProcessesPayload {
         let cache_cleanup_threshold = name_cache_cleanup_threshold();
 
         if total_count > proc_cache.names.len() + cache_cleanup_threshold {
+            // `now` is only consumed by the `tracing::debug!` below, so gate
+            // the binding with the same cfg as its consumer. Without this,
+            // a non-logging build (the default) emits an unused-variable
+            // warning. The Linux CI doesn't catch it because this block lives
+            // in the `#[cfg(not(target_os = "linux"))]` collect_processes_all —
+            // the warning only surfaces on the Windows build matrix.
+            #[cfg(feature = "logging")]
             let now = std::time::Instant::now();
             proc_cache
                 .names