Advocate Program Long-Call Growth

UnitedHealth Group runs a member support program where policy holders call an advocate for help with claims, benefits, drug coverage, pre-authorisation, medical records, emergency assistance and the member portal. Each call is recorded in the `callers` table. To track the program, the analytics team wants the month-over-month growth in the number of long calls. A long call is any call lasting strictly more than 5 minutes (more than 300 seconds); a call of exactly 300 seconds is not a long call. Write an SQL query that returns `call_year` and `call_month` (both as numbers), and `growth_pct`: the percentage change in the number of long calls compared with the previous month, rounded to 1 decimal place. The first month has no previous month, so its growth must be NULL. Order the results by `call_year` ascending, then `call_month` ascending.