feat(sub): subscription logic (pre release)

db/models/subscription_addons.py

@@ -0,0 +1,23 @@
+from typing import TYPE_CHECKING
+
+from sqlalchemy import INTEGER, ForeignKey
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from db.base import Base
+
+if TYPE_CHECKING:
+    from db.models import Subscription
+
+
+class SubscriptionAddon(Base):
+    __tablename__ = "subscription_addons"
+
+    id: Mapped[int] = mapped_column(
+        INTEGER, nullable=False, unique=True, autoincrement=True, primary_key=True
+    )
+    subscription_id: Mapped[int] = mapped_column(ForeignKey("subscriptions.id"), nullable=False)
+    addon_id: Mapped[str] = mapped_column(ForeignKey("addons.id"), nullable=False)
+
+    subscription: Mapped["Subscription"] = relationship(
+        "Subscription", back_populates="addons", lazy="selectin"
+    )