SQLC does not create __init__.py file

[Goldziher]

Issue: The generated output package does not have an __init__.py file.

This file makes the output into a Python package; otherwise, it's just a bunch of files. Furthermore, the imports in the files do not work correctly without it.

The __init__.py file should include all the exports of the generated code and an __all__ = [...] variable inside the file (otherwise linters, mypy and intellij will complain).