rust-dirstate: call rust dirstatemap from Python Since Rust-backed Python classes cannot be used as baseclasses (for rust-cpython anyway), we use composition rather than inheritance. This also allows us to keep the IO operations in the Python side, removing (for now) the need to rewrite VFS in Rust, which would be a heavy undertaking. Differential Revision: https://phab.mercurial-scm.org/D6634

rust-dirstate: rust-cpython bridge for dirstatemap This change also showcases the limitations of the `py_shared_ref!` macro. See the previous commit 'rust-dirstate: rust implementation of dirstatemap` for an explanation for the TODOs in the code. Differential Revision: https://phab.mercurial-scm.org/D6633

rust-dirstate: rust implementation of dirstatemap The `dirstatemap` is one of the last building blocks needed to get to a `dirstate.walk` Rust implementation. Disclaimer: This change is part of a big (10) series of patches, all of which started as one big changeset that took a long time to write. This `dirstatemap` implementation is a compromise in terms of complexity both for me and for the reviewers. I chose to submit this patch right now because while it is not perfect, it works and is simple enough (IMHO) to be reviewed. The Python implementation uses a lot of lazy propertycaches, breaks encapsulation and is used as an iterator in a lot of places, all of which dictated the somewhat unidiomatic patterns in this change. Like written in the comments, rewriting this struct to use the typestate pattern might be a good idea, but this is a good first step. Differential Revision: https://phab.mercurial-scm.org/D6632