Top-Spending Customers by Country

The marketing department is planning a rewards initiative and needs to know which customers have spent the most in each country. They want to see, for every country, the name of the country, the name of the customer(s) who have spent the highest total amount (calculated as the sum of quantity times unit_price for all their orders), and the total amount spent. Include only countries where at least one order has been placed. If more than one customer in a country shares the top spending amount, include them all.