fix(tests): fix API test expectations, remove warnings, and clean async test structure

[Vishmayraj]

Summary

This PR improves the api/tests suite by aligning tests with current endpoint behavior, removing warnings, and cleaning up async test implementations.

Changes Included

• Updated test_create_user_unexpected_error_returns_400_without_details to match the current create_user response behavior (400 instead of 500) while still verifying that internal exception details are not exposed.
• Fixed test_connection_always_closed_even_on_exception to properly simulate a post-acquisition failure path and validate cleanup behavior without coroutine/runtime warnings.
• Removed unnecessary global asyncio markers from synchronous tests in test_set_role_sql_safety.py.
• Refactored async tests in test_set_role_sql_safety.py to use native pytest.mark.asyncio + await instead of asyncio.run(...).

Result

• Full suite passes locally.
• Warning count reduced to zero.
• Test behavior now better reflects actual runtime paths and expected responses.

Additional Note

The api/tests directory is currently somewhat fragmented in structure and repeats setup logic (environment variables, path setup, fixtures). If helpful, I’d be happy to contribute a follow-up PR to gradually migrate these tests into the repository root tests/ directory so they can share conftest.py, common fixtures, and a more maintainable layout.