style: cargo fmt under rustfmt 1.9.0 (toolchain update 2026-07-08)

Six diffs across four files: the 2026-07-08 stable toolchain update
(rustc 1.96.1 / rustfmt 1.9.0) re-flags code that was fmt-clean when
committed under the previous rustfmt. No semantic change.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/transport_loopback.rs

@@ -304,7 +304,9 @@ async fn connection_stats_report_a_direct_path_with_live_counters() {
     assert_eq!(info.remote_addr, s2.remote_addr);
     assert!(info.rtt_ms < 1000, "localhost RTT should be sane");
     assert!(
-        info.up_kbps.expect("same path + positive window has a rate") > 0.0,
+        info.up_kbps
+            .expect("same path + positive window has a rate")
+            > 0.0,
         "audio was flowing, so the upstream rate must be non-zero"
     );
 }