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.