Next-Month Cohort Retention

Meta's growth team measures month-1 retention. Users are grouped into cohorts by the calendar month of their `signup_date`. A user is retained if they have at least one activity in the calendar month immediately after their signup month (for a December signup, that is January of the next year). Activity in the signup month itself, or in later months while skipping the next month, does not count, and multiple activities in the same month count only once. Return `cohort_month` (formatted `YYYY-MM`), `cohort_size`, `retained_users` and `retention_pct` (retained / cohort size * 100, rounded to 2 decimals) for every cohort. Order the results by `cohort_month` ascending.