Refactor test files for improved readability and consistency

- Removed unnecessary blank lines and adjusted formatting in test files.
- Ensured consistent use of commas in function calls and assertions across various test cases.
- Updated import statements for better organization and clarity.
- Enhanced mock setups in tests for better isolation and reliability.
- Improved assertions to follow a consistent style for better readability.

app/models/credit_transaction.py

@@ -26,4 +26,4 @@ class CreditTransaction(BaseModel, table=True):
     metadata_json: str | None = Field(default=None)
 
     # relationships
-    user: "User" = Relationship(back_populates="credit_transactions")
+    user: "User" = Relationship(back_populates="credit_transactions")