tests: rename _bytespath() to _sys2bytes() and _strpath() to _sys2str()
The names were not general enough because e.g. _strpath() was used for
converting IP addresses.
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true