rust-dirstate: pass dirstate tracked key from the requirements We will make use of this with the `hg update` fastpath

rust-files: check for empty manifests caused by narrow Explanations inline

rust-repo: don't use on-disk dirstate parents in v1 This mistake was not causing any problems yet since we were never updating parents from Rust code. This is about to change, so let's fix it.

rust-cpython: add a util to get a `Repo` from a python path I suspect this will not be the last time we need to do something like this.