Products Driving 80% of Revenue

Amazon merchandising applies the Pareto principle: which top products generate the first 80% of revenue? Rank products by `revenue` descending (ties broken by `product_id` ascending) and accumulate revenue down the ranking. A product belongs to the core set if the cumulative revenue of all products ranked strictly above it is less than 80% of total revenue; equivalently, the core set is the smallest set of top products whose cumulative revenue reaches at least 80%. Return `product_name`, `revenue` and `cumulative_pct` (cumulative revenue including this product as a percentage of total revenue, rounded to 2 decimals) for the core set. Order the results by `revenue` descending, then `product_id` ascending.