rust-index: document safety invariants being upheld for every `unsafe` block
We've added a lot of `unsafe` code that shares Rust structs with Python.
While this is unfortunate, it is also unavoidable, so let's at least
systematically explain why each call to `unsafe` is sound.
If any of the unsafe code ends up being wrong (because everyone screws up
at some point), this change at least continues the unspoken rule of always
explaining the need for `unsafe`, so we at least get a chance to think.
[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