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.

rust-repo: add a method to set the current parents This will be useful when we start writing an `hg update` fastpath.

rust-repo: add a method to get a `Node` from a `Revision` to the `Repo` This is going to be more and more useful as we start writing higher-level code

rust-utils: move the `filesystem_now` function to a util This is going to be useful for an upcoming `hg update` fastpath.