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.

rust-files: also return filenode and flags when listing a revision's files This is going to be useful when implementing parts of `update` and makes it so we don't have to fetch the manifest and each entry twice.

rust-manifest: encode flags as `Option<NonZeroU8>` This makes the compiler use the niche optimization for all flags: since 0 is not a valid representation of any flags, we can use 0 as a replacement for `None`, which reduces memory footprint and could yield a little performance improvement over many iterations.