style: reformat all files with `black`

poetry.lock

pycgtool/__main__.py

pycgtool/bondset.py

pycgtool/forcefield.py

pycgtool/frame.py

pycgtool/functionalforms.py

pycgtool/mapping.py

pycgtool/parsers/__init__.py

pycgtool/parsers/cfg.py

pycgtool/parsers/itp.py

pycgtool/util.py

pyproject.toml

tests/test_bondset.py

tests/test_forcefield.py

tests/test_frame.py

tests/test_functionalforms.py

tests/test_mapping.py

tests/test_parsers_cfg.py

tests/test_parsers_topology.py

tests/test_pycgtool.py