SAN FRANCISCO — The champagne buzz is still wearing off from the party in Boston and a parade is planned in San Francisco Monday to celebrate the Warriors’ fourth NBA title in eight years. But the Warriors have one eye looking forward to free agency that starts July 1. This championship proved that, even with the core in their mid-30s, the contention window is still wide open. Pressure is on the front office to keep the roster well-equipped to run it back in 2023 and beyond. Nine Warriors will be free agents, seven unrestricted: Gary Payton II, Andre Iguodala, Kevon Looney, Otto Porter Jr., Ne…