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.

db/models/bills.py

@@ -0,0 +1,28 @@
+from typing import TYPE_CHECKING
+
+from sqlalchemy import BIGINT, INTEGER, Enum, ForeignKey
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from db.base import Base
+from misc.pally import BillStatus
+
+if TYPE_CHECKING:
+    from db.models.users import User
+
+
+class Bill(Base):
+    __tablename__ = "bills"
+
+    id: Mapped[int] = mapped_column(
+        BIGINT, autoincrement=True, unique=True, nullable=False, primary_key=True
+    )
+    creator_id: Mapped[int] = mapped_column(BIGINT, ForeignKey("users.id"), nullable=False)
+    amount: Mapped[int] = mapped_column(INTEGER, nullable=False)
+    status: Mapped[BillStatus] = mapped_column(
+        Enum(BillStatus), nullable=False, default=BillStatus.NEW
+    )
+
+    user: Mapped["User"] = relationship(
+        "User",
+        back_populates="bills",
+    )