Add tests for sound repository, user OAuth repository, credit service, and credit decorators

- Implement comprehensive tests for SoundRepository covering CRUD operations and search functionalities.
- Create tests for UserOauthRepository to validate OAuth record management.
- Develop tests for CreditService to ensure proper credit management, including validation, deduction, and addition of credits.
- Add tests for credit-related decorators to verify correct behavior in credit management scenarios.

app/models/credit_transaction.py

@@ -0,0 +1,29 @@
+"""Credit transaction model for tracking credit usage."""
+
+from typing import TYPE_CHECKING
+
+from sqlmodel import Field, Relationship
+
+from app.models.base import BaseModel
+
+if TYPE_CHECKING:
+    from app.models.user import User
+
+
+class CreditTransaction(BaseModel, table=True):
+    """Database model for credit transactions."""
+
+    __tablename__ = "credit_transaction"  # pyright: ignore[reportAssignmentType]
+
+    user_id: int = Field(foreign_key="user.id", nullable=False)
+    action_type: str = Field(nullable=False)
+    amount: int = Field(nullable=False)  # Negative for deductions, positive for additions
+    balance_before: int = Field(nullable=False)
+    balance_after: int = Field(nullable=False)
+    description: str = Field(nullable=False)
+    success: bool = Field(nullable=False, default=True)
+    # JSON string for additional data
+    metadata_json: str | None = Field(default=None)
+
+    # relationships
+    user: "User" = Relationship(back_populates="credit_transactions")