Check token estimate filtering directly on the tracing subscriber (#50054)

## What changed

Update `post_sampling_token_estimate_is_disabled_by_always_on_sinks` to register explicit event metadata with the subscriber and assert that its interest is `never`. This replaces the scoped default subscriber and global interest-cache rebuild with a direct check of the configured logging layers.

GitOrigin-RevId: 7c4ecd9c4adef148fd222394ad1ad326e8033d95

codex-rs/core/src/session/turn_tests.rs

@@ -46,16 +46,18 @@ fn post_sampling_token_estimate_is_disabled_by_always_on_sinks() {
         .with(feedback.logger_layer())
         .with(tracing_subscriber::fmt::layer().with_filter(codex_state::log_db::default_filter()));
 
-    tracing::subscriber::with_default(subscriber, || {
-        tracing::callsite::rebuild_interest_cache();
-        assert!(!tracing::event_enabled!(
-            target: POST_SAMPLING_TOKEN_ESTIMATE_TARGET,
-            tracing::Level::TRACE,
-            turn_id,
-            estimated_token_count,
-            message
-        ));
-    });
+    static METADATA: tracing::Metadata<'static> = tracing::metadata! {
+        name: "post sampling token estimate filter probe",
+        target: POST_SAMPLING_TOKEN_ESTIMATE_TARGET,
+        level: tracing::Level::TRACE,
+        fields: &["turn_id", "estimated_token_count", "message"],
+        callsite: &CALLSITE,
+        kind: tracing::metadata::Kind::EVENT.hint(),
+    };
+    static CALLSITE: tracing::callsite::DefaultCallsite =
+        tracing::callsite::DefaultCallsite::new(&METADATA);
+
+    assert!(tracing::Subscriber::register_callsite(&subscriber, &METADATA).is_never());
 }
 
 #[tokio::test]