Checkpoint: One-Pass Analytics

Implement the analytics engine described in the checkpoint: ``csharp public record Sale(string Customer, string Category, decimal Amount); static decimal Revenue(IEnumerable<Sale> sales); static string BestCategory(IEnumerable<Sale> sales); static List<string> CustomerMatrix(IEnumerable<Sale> sales, IEnumerable<string> customers); static string Run(IEnumerable<Sale> sales, IEnumerable<string> customers); // Run format: "revenue=<r>;best=<c>;|name=total|name=total..." ``