The longest silence between two flights

The win-back team wants to understand lapsed travellers. For every passenger with at least two flights, they look at the gap in calendar days between one completed flight and the next one that passenger took, and keep the largest gap. Cancelled flights are not flights the passenger took. Use only the date part of sched_dep (the first 10 characters) when counting days.

Task: return passenger (name), flights (how many completed flights the passenger took) and longest_gap_days (an integer: the largest number of days between two consecutive flights of that passenger). Only passengers with 2 or more completed flights appear. Keep the 10 largest gaps, sorted by longest_gap_days from high to low, then passenger A to Z.