style: apply cargo fmt across the crate (A20)

The repo never enforced rustfmt, so formatting had drifted broadly. This is a
single mechanical `cargo fmt` pass over the whole crate (no behavioral change;
lib suite green, 493 passed). Going forward fmt should be enforced (planned CI
fmt --check step). Part of the 0.6.1 hygiene pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/reconnect_eviction.rs

@@ -62,7 +62,7 @@ async fn evicted_within(
             Ok(Some(UiEvent::PeerConnectionFailed { id })) if id == peer => return true,
             Ok(Some(_)) => continue, // ignore PeerConnecting / PeerConnected / PeerLeft
             Ok(None) => return false, // channel closed
-            Err(_) => return false,   // timed out — no eviction
+            Err(_) => return false,  // timed out — no eviction
         }
     }
 }
@@ -80,7 +80,7 @@ async fn left_within(
             Ok(Some(UiEvent::PeerLeft { id })) if id == peer => return true,
             Ok(Some(_)) => continue, // ignore PeerConnecting / PeerConnected
             Ok(None) => return false, // channel closed
-            Err(_) => return false,   // timed out — no leave
+            Err(_) => return false,  // timed out — no leave
         }
     }
 }