import: read X-Mercurial-Node email header to determine nodeid
This would be useful to import and obsolete patches sent using 'hg email
--plain', using evolve's --obsolete option of 'hg import'.
If email body contains Mercurial patch header ('# HG changeset patch'
block), nodeid parsed from X-Mercurial-Node header will still be
overridden by respective value found in body.
[tool.black]
line-length = 80
exclude = 'build/|wheelhouse/|dist/|packages/|\.hg/|\.mypy_cache/|\.venv/|mercurial/thirdparty/|hgext/fsmonitor/pywatchman/|contrib/python-zstandard/'