rust: Read dirstate from disk in DirstateMap constructor...
rust: Read dirstate from disk in DirstateMap constructor
Before this changeset, Python code first creates an empty `DirstateMap` Rust
object, then immediately calls its `read` method with a byte string of the
contents of the `.hg/dirstate` file.
This makes that byte string available to the constructor of `DirstateMap`
in the hg-cpython crate. This is a first step towards enabling parts of
`DirstateMap` in the hg-core crate to borrow from this buffer without copying.
Differential Revision:
https://phab.mercurial-scm.org/D10556
