feat(billing): implement billing module with Stripe and Mercado Pago integration

- Add Stripe and Mercado Pago providers for handling subscriptions.
- Create billing repository and access services for managing billing records.
- Implement webhook handlers for processing events from Stripe and Mercado Pago.
- Add routes for checkout, canceling subscriptions, and retrieving billing status.
- Introduce billing status management with appropriate state transitions.
- Create tests for billing functionalities including webhook idempotency and provider resolution.
- Document the billing module architecture, environment variables, and API endpoints.

apps/backend/test/support/prisma.mock.ts

@@ -27,6 +27,8 @@ export const dbMock = {
   courtBookingLog: prismaMock.courtBookingLog,
   courtAvailability: prismaMock.courtAvailability,
   courtPriceRule: prismaMock.courtPriceRule,
+  complexBilling: prismaMock.complexBilling,
+  billingEvent: prismaMock.billingEvent,
   $transaction: transactionMock,
 };