changing-files: cache the various property
We are going to start using them more having some basic caching would be good.
The focus is not about performance yet, however avoid some easy N² trap seems
reasonable.
Differential Revision: https://phab.mercurial-scm.org/D9112
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true