rust-index: check rindex and cindex return the same get_rev This is a temporary safeguard while we synchronize both indexes.

rust-index: synchronize remove to Rust index Future steps will bring the two indexes further together until we can rip the C index entirely when running Rust code.

rust-index: remove `__setitem__` method from the mixed index This is not defined on the Python or C one, and isn't used anywhere.

rust-index: check equality between rust and cindex for `__len__`

rust-index: synchronize append method We now append to the Rust index just as we do to the C index. Future steps will bring the two indexes further together until we can rip the C index entirely when running Rust code.

rust-revlog: teach the revlog opening code to read the repo options This will become necessary as we start writing revlog data from Rust.

rust-index: pass data down to the Rust index This will allow us to start keeping the Rust index synchronized with the cindex as we gradually implement more and more methods in Rust. This will eventually be removed.

rust-index: add append method This is the first time the Rust index has any notion of mutability. This will be used in a future patch from Python, to start synchronizing the Rust index and the C index.