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/user.py

@@ -6,6 +6,7 @@ from sqlmodel import Field, Relationship
 from app.models.base import BaseModel
 
 if TYPE_CHECKING:
+    from app.models.credit_transaction import CreditTransaction
     from app.models.extraction import Extraction
     from app.models.plan import Plan
     from app.models.playlist import Playlist
@@ -35,3 +36,4 @@ class User(BaseModel, table=True):
     playlists: list["Playlist"] = Relationship(back_populates="user")
     sounds_played: list["SoundPlayed"] = Relationship(back_populates="user")
     extractions: list["Extraction"] = Relationship(back_populates="user")
+    credit_transactions: list["CreditTransaction"] = Relationship(back_populates="user")