Add __init__.py files to convert the folders to python module.

This allows one to run `pytest` in the root folder to trigger all the
tests, instead of needing to modify PYTHONPATH environment variable.

.github/workflows/run_pytest.yaml

@@ -12,16 +12,16 @@ jobs:
     runs-on: ubuntu-latest
     steps:
           - uses: actions/checkout@v4
-          
+
           - name: Set up Python
             uses: actions/setup-python@v5
             with:
-              python-version: '3.9'   
-              
+              python-version: '3.9'
+
           - name: Install dependencies
             run: |
               python -m pip install --upgrade pip
               pip install pytest
               pip install requests
           - name: Test with pytest
-            run: PYTHONPATH="${PYTHONPATH}:${pwd}" pytest
+            run: pytest