The Capacitated Vehicle Routing Problem (CVRP) is a combinatorial optimization challenge where vehicles with limited capacity must deliver goods from a central depot to multiple customer locations, minimizing total travel distance while respecting vehicle capacity constraints. 
We use Policy Optimization with Multiple Optima (POMO) to solve this problem, where a neural network policy generates multiple solutions from different starting points simultaneously, sharing parameters across all starting positions. 
Your task is to evolve a `heuristics` function that generates an attention bias matrix to guide the model's decoder attention, with the goal of minimizing the total distance traveled across all vehicle routes while respecting capacity constraints (called "score" or "objective" of solution).