Refactor E2E tests and fixtures for improved readability and consistency

- Reformatted assertions in `test_database_workflows.py` for better readability.
- Refactored `postgres_url` transformation logic in `conftest.py` for improved clarity.
- Adjusted import handling in `test_api_contracts.py` to streamline usage of Hypothesis and Schemathesis libraries.

backend/tests/e2e/conftest.py

@@ -122,9 +122,9 @@ def async_postgres_url(postgres_url) -> str:
     Testcontainers returns postgresql+psycopg2:// format.
     """
     # Testcontainers uses psycopg2 by default, convert to asyncpg
-    return postgres_url.replace("postgresql+psycopg2://", "postgresql+asyncpg://").replace(
-        "postgresql://", "postgresql+asyncpg://"
-    )
+    return postgres_url.replace(
+        "postgresql+psycopg2://", "postgresql+asyncpg://"
+    ).replace("postgresql://", "postgresql+asyncpg://")
 
 
 @pytest_asyncio.fixture