Betsy Beers looks pretty nonchalant someone in the middle of the TV pilot race. In her temporary Summer Street office, she leans back, at ease, surrounded by bulletin boards that are covered in pictures of 19th century costumes and buildings. Beers has only three weeks to finish what she’s started - a pilot for a period drama called “Gilded Lilys’’ - but she’s used to this pace. After all, she and her collaborator, Shonda Rhimes, have done this successfully over and over again, with shows like “Grey’s Anatomy,’’ “Private Practice,’’ and now “Scandal,’’ which debuts Thursday.