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/billing.py

@@ -0,0 +1,13 @@
+from dataclasses import dataclass
+from enum import Enum
+
+
+class BillingProviders(Enum):
+    PALLY = "pally"
+
+
+@dataclass
+class BillingContext:
+    amount: int
+    bill_id: int | None = None
+    provider: BillingProviders | None = BillingProviders.PALLY