...Holy Mary mother of God, Pray for us sinners now and at the hour of our death amen.
Except that this isn’t the Rosary. ;)
True, not part of the decades but it's at the end, and would have to be prayed by our Mary fearing brethren if they dared to meditate on the Gospel via the rosary.
They are entirely optional. Some include them, some do not.
There’s also a prayer to St. Michael the Archangel, but I’ve never seen a protestant argue that we are worshiping St. Michael.
I don’t really see how the rosary is ‘praying to mary’, when it acknowledges Christ as Lord.