Mark David Rich and famous folk are notorious for their itchy real estate feet, buying and selling multimillion-dollar homes with the same ease and alacrity as mere financial mortals might, say, buy a new pair of shoes or change out the baking soda box in the fridge. One exception, at least in San Francisco, is Hollywood veteran Winona Ryder, who’s owned the same home in the city’s affluent Cow Hollow neighborhood for 25 years.