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.

rust: improve `InvalidRevision` error message I encountered this when debugging earlier and felt like we were losing some information along the way, which we were!

rust-dirstate: use a struct as arguments for the high-level `reset_state` This makes the interface a lot clearer at the call site and prevents silly mistakes, as an API with a bunch of booleans is prone to errors. This refactor adds a `from_empty` parameter for a fast-path when resetting and entry we're sure does not exist. It will be used in the upcoming update Rust fastpath, and was not split to prevent more churn.

rust: implement `From<SparseConfigWarning>` for `HgError` This will be useful in a future patch to avoid a lot of boilerplate.

rust-hg-cpython: add an `HgProgressBar` util This will be the entry point for all progress bars from a Python context in upcoming patches. Like the `Progress` trait, this is subject to change once we have more use cases, but this is good enough for now.

rust: add `Progress` trait for progress bars This will be used in the next few changes to introduce a progress bar for the `hg update` fastpath.

rust-files: separate the listing of files from a revset and a revision We won't need to parse a revset all the time, and an upcoming patch will make use of this new util.

rust-files: add a `Sync` bound to the matcher This enables us to use this code in multithreaded environements, which we very much want to do.