fix(chain): Copy returns wrong pointer, connection leaks in Connect/Handshake, deferred cancel accumulation in retry loops

- transport.go: Copy() returned original pointer instead of the allocated copy,
  causing data races and incorrect routing for multiplexed chains.
- route.go: Connect and Handshake failures in intermediate nodes leaked the
  returned connection. Handshake fix preserves the original Connect result
  (guaranteed non-nil) and closes both the Handshake return value and input.
- router.go: defer cancel() inside retry loops accumulated context timers
  across iterations. Wrapped each loop body in an IIFE so defer scopes
  per-iteration and timers are released immediately.

chain/route.go

@@ -271,20 +271,29 @@ func (r *chainRoute) connect(ctx context.Context, logger logger.Logger) (conn ne
 		}
 		cc, err = preNode.Options().Transport.Connect(ctx, cn, "tcp", addr)
 		if err != nil {
+			if cc != nil {
+				cc.Close()
+			}
 			cn.Close()
 			if marker != nil {
 				marker.Mark()
 			}
 			return
 		}
-		cc, err = node.Options().Transport.Handshake(ctx, cc)
+		var cc2 net.Conn
+		cc2, err = node.Options().Transport.Handshake(ctx, cc)
 		if err != nil {
+			if cc2 != nil {
+				cc2.Close()
+			}
+			cc.Close()
 			cn.Close()
 			if marker != nil {
 				marker.Mark()
 			}
 			return
 		}
+		cc = cc2
 		if marker != nil {
 			marker.Reset()
 		}