Caesars Interactive Entertainment has toppled Zynga as the No. 1 publisher of social casino games, according to a report by research firm Eilers Research. That shows that the social casino game market, which is now worth $1.2 billion worldwide, is becoming a lot more competitive thanks to growth in demand, increased startup activity, and a series of high-profile acquisitions. Caesars is one of the world’s largest legal gambling companies. It acquired Israel’s Playtika in 2011 and picked up popular social games such as Slotomania. Now, that title as well as Slotomania Adventures, Bingo Blitz (acquired with the purchase of Buffalo…