rust-index: moved constructor in separate impl block
with the upcoming addition of the nodemap logic, it's going to become
more complicated.
Being in the separate impl block has the advantage to be subject to rustfmt,
whereas code inside macro calls isn't.
Differential Revision: https://phab.mercurial-scm.org/D8153
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true