ao_pipewire: log sample queueing

This allows us to more easily see the datapath from mpv to pipewire.

We know how often the callbacks are triggered, how big the buffers are
and how much data mpv provides to pipewire.

audio/out/ao_pipewire.c

@@ -183,6 +183,8 @@ static void on_process(void *userdata)
     }
 
     pw_stream_queue_buffer(p->stream, b);
+
+    MP_TRACE(ao, "queued %d of %d samples\n", samples, nframes);
 }
 
 static void on_param_changed(void *userdata, uint32_t id, const struct spa_pod *param)