Global refactoring of the project to use poetry and implement tests,

fixing bugs, changing the handling of dto and db models, preparing to
add new functionality

tests/test_relationships.py

@@ -0,0 +1,12 @@
+import pytest
+from alembic import command
+from alembic.config import Config
+from fastapi.testclient import TestClient
+from sqlmodel import select, delete, Session
+
+from library_service.main import app
+from tests.test_misc import setup_database
+
+client = TestClient(app)
+
+#TODO: add tests for relationships endpoints