phases: gather the logic for phasesets update in a single method
This logic is duplicated around for no good reason, we gather it in a single
place.
The conditional is the new function are a bit weird as we about going to extend it soon.
[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