feat: implement billing system with Pally integration

- Added billing models and repository for handling bills.
- Introduced BillingService to manage payment initiation and bill creation.
- Updated user service to remove ticket-related functionality.
- Refactored settings to include new billing-related fields.
- Removed ticket-related handlers and schemas.
- Added new billing handlers for processing payments.
- Updated database schema with new bills table and status enum.
- Enhanced utility functions to calculate prices considering discounts.
- Introduced prehandling for non-private messages.
- Updated main application to initialize new billing services and repositories.

schemas/subscriptions.py

@@ -16,3 +16,4 @@ class SubscriptionPlan(BaseModel):
     devices: int = settings.min_devices
     duration: SubscriptionDuration = SubscriptionDuration.MONTH
     whitelists: bool = False
+    discount: float = 1