✅ test(database.py): add tests for CRUD operations on Flow model
The new fixtures added to conftest.py are session and client fixtures. These fixtures are used to create a test database and a test client for testing the database. The tests added to test_database.py test the CRUD operations on the Flow model. The tests include creating a flow, reading all flows, reading a single flow, updating a flow, and deleting a flow. These tests ensure that the database is working as expected and that the API endpoints for the Flow model are functioning correctly.
