feat: creating mogodb and postgres mock instance in checkpoint test (#561)

* fix: using mongomock for the checkpoint test

* Add postgres mock setting to the unit test

* Added utils file of postgres_mock_utils

* fixed the runtime loading error of deerflow server

.github/workflows/unittest.yaml

@@ -54,7 +54,7 @@ jobs:
     - name: Run test cases with coverage
       run: |
         source .venv/bin/activate
-        TAVILY_API_KEY=mock-key make coverage
+        TAVILY_API_KEY=mock-key DB_TESTS_ENABLED=true make coverage
 
     - name: Generate HTML Coverage Report
       run: |