streamSubscribe panics on NewConsumer failure; unsynced stats counters

Two bugs in the amqp091 stream path:

• streamSubscribe ignores the error from StreamConnection.NewConsumer and then unconditionally calls consumer.Close(). When the consumer fails to construct it returns (nil, err), and the subsequent Close() panics the goroutine. The error should be surfaced as *pb.Error and the increment/Close path skipped.
• Stats() and connectionCleaner read produced, consumed, and ActiveStreams as plain int64s, but writers use atomic.AddInt64. The reads should use atomic.LoadInt64 to remove the data race.

Start at the streamSubscribe, Stats(), and connectionCleaner entry points. Trace the NewConsumer failure path and the atomic writes to produced, consumed, and ActiveStreams; done means the failure returns a *pb.Error without panicking and the counter reads are race-safe.