rust-index: add support for `del index[r]`
Only the `del index[r:]` syntax was supported, but the comment said otherwise.
It's not actually used in core code, but the C index supports it.
[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