Restaurant construction has been moving along s-l-o-w-l-y at Park Potomac, where two new eateries that were supposed to arrive before the holidays have been delayed until next year. Filicori Zecchini, the Italian coffee house and cafe, is now looking to open in January or February. Gringos & Mariachis, a Mexican concept from the owners of Bethesda’s Olazzo, is tentatively set for March. And Addie’s, the new incarnation of the beloved Rockville Pike restaurant, should follow sometime this spring.