rust-index: renamed `MixedIndex` as `Index` It is simply not mixed any more, hence the name had become a future source of confusion.

rust-index: stop instantiating a C Index The only missing piece was the `cache` to be returned from `revlog.parse_index_v1_mixed`, and it really seems that it is essentially repetition of the input, if `inline` is `True`. Not worth a Rust implementation (C implementation is probably there for historical reasons).

rust-revlog: using the ad-hoc `NodeTree` in scmutil Now that we have an independent `NodeTree` class able to work natively on the pure Rust index, we use it in `mercurial.scmutil`, with automatic invalidation after mutation of the index. This code path is tested by `test-revisions.t` and `test-template-functions.t`

rust-revlog: add invalidation detection to `NodeTree` class This will be useful for callers, such as `scmutil` who reuse a `NodeTree` instance as a cache. They would otherwise get hard errors if any mutation of the index occurred since instantiation. This is something the C index does not provide.