vfs: make the default opener mode binary The default was already binary for `abstractvfs`, and the `vfs` implementation adds binary mode if the caller didn't supply it. Therefore, it should be safe for all vfs objects (and I don't think we want text reads anyway).

[build-system]
requires = ["setuptools", "wheel"]

[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true