Add the coconut milk, sugar, milk, and heavy cream and bring slowly to a boil, stirring gently as you do so. Add the zest of 1 lime, then taste, adding more if you like. Pour in the rice and mix well. Bring to a boil, reduce to a simmer, and cook gently for 20 minutes, stirring constantly, until most of the milk mixture is absorbed and the rice is softened.