What would you think about implementing this in #grain

Payment Models

1. Pay-Once Model

- Description: Single payment for permanent relay access

- Use Case: Users who want lifetime access

- Implementation: Simple whitelist addition after payment confirmation

2. Subscription Model

- Description: Time-based access with prorated refunds

- Use Case: Users who want temporary access with flexibility

- Features:

- Configurable duration (days, months, years)

- Prorated refunds based on unused time

- Automatic whitelist removal on expiry

- Immediate refund processing

3. Pay-Per-Use Model

- Description: Credit-based system with per-event charges

- Use Case: Light users who want granular control

- Features:

- Deposit system with balance tracking

- Per-kind pricing (different costs for different event types)

- Event Category-based pricing (regular, replaceable, etc)

- Real-time balance deduction

- Withdrawal of unused credits