Avoid Double Counting for SMS + Email Alerts

I’ve noticed an issue with how alert sign-ups are counted. When a customer subscribes to an alert with both their email and phone number, Stoq currently counts this as two separate alerts (quantity = 2).

In reality, it’s the same person requesting a single alert. This double counting makes it difficult to accurately evaluate demand and plan stock reorders.

Feature request:
Please adjust the logic so that when a customer signs up with both email and phone, it only counts as one alert request (quantity = 1). Alternatively, provide an option to set SMS alerts with quantity = 0 to avoid inflating the demand calculation.

This change would make the reporting much more accurate for inventory planning.