Add unit-tests

.gitignore

mypy.ini

pytest.ini

src/rechunk_data/__init__.py

src/rechunk_data/__init__.pyi

src/rechunk_data/tests/conftest.py

src/rechunk_data/tests/test_cli.py

src/rechunk_data/tests/test_rechunk_netcdf.py

src/rechunk_data/tests/test_rechunking.py

src/rechunk_data/tests/test_search_files.py