copies: extract value comparison in the python copy tracing This mirror what we did in the Rust code. This is useful to prepare rework for this comparison logic that we will need to handle more advanced chaining cases (when merges are chained). Differential Revision: https://phab.mercurial-scm.org/D9590

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