CI/CD update: successful cosim_example.py execution from built package & fixed file path issues

[amandamalk0601]

Updated the CI/CD pipeline to:

• Use Poetry to build and install a package from the latest main branch code.
• Test the installed package by running the example scenario cosim_example.py, verifying file paths are set correctly.

Changes made:

• Modified pyproject.toml to include examples/ and tests/ when building the package.
• Fixed file path issues in _data.py to correctly locate the solar and carbon data files when executing example scenario from the installed package.

The file path issues were resolved using the files function from importlib.resources, which is natively available in Python from version 3.9 onwards. For compatibility with Python 3.8, the external importlib_resources library was added to pyproject.toml.

[marvin-steinke]

cool beans