Count active monthly donors rather than subscriptions

For GiveCampus reporting.

Use the Subscription Report, not the installment report, and include subscription state, recurring frequency/period, subscription type and constituent identifier. Choose a date range broad enough to include older subscriptions still active today. Filter to active ordinary recurring gifts with monthly billing, including fixed-month terms where the period is represented as limited_months; exclude pledges and canceled/ended/failed commitments for this definition. Count distinct constituent IDs after reviewing missing IDs and duplicate donor identities, rather than counting subscription rows or payments. One donor can hold multiple active monthly subscriptions. If “actively giving” means a successful recent payment as well as an active schedule, additionally reconcile the installment report for the chosen period.