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.

services/billing_service.py

@@ -0,0 +1,41 @@
+import logging
+
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from config import settings
+from misc.pally import BillCreateResponse, Currency, PallyAPIError, PallyClient
+from repositories import UserRepository
+from repositories.bills import BillsRepository
+
+logger = logging.getLogger(__name__)
+
+
+class BillingService:
+    def __init__(self, user_repository: UserRepository, bills_repository: BillsRepository) -> None:
+        self.user_repository = user_repository
+        self.bills_repository = bills_repository
+
+    async def pally_initiate_payment(
+        self,
+        session: AsyncSession,
+        pally_client: PallyClient,
+        *,
+        user_id: int,
+        amount: int,
+        currency: Currency | None = Currency.RUB,
+    ) -> BillCreateResponse | None:
+        db_bill = await self.bills_repository.create(session, creator_id=user_id, amount=amount)
+
+        try:
+            async with pally_client as pl:
+                bill = await pl.bills.create(
+                    db_bill.amount,
+                    shop_id=settings.pally_shop_id,
+                    order_id=db_bill.id,
+                    currency_in=currency,
+                )
+        except PallyAPIError:
+            logger.exception("caught an exception while trying to create a bill:")
+            return None
+
+        return bill