branchcache: stop using `copy(…)` in `replace(…)` The `copy` method is mostly used for a filter level to inherit the branchmap from a subset. So we stop using (abusing) it in "replace" to ensure `copy` is used only for inheritance purposes. Since `replace` is a method of the BranchMapCache, it seems fine to do lower level operation there.

[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