rust: Use the DisplayBytes trait in config printing This is similar to `std::fmt::Display`, but for arbitrary bytes instead of Unicode. Writing to an abstract output stream helps avoid allocating intermediate `Vec<u8>` buffers. Differential Revision: https://phab.mercurial-scm.org/D9966

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