rust: Switch to the memmap2-rs crate https://github.com/RazrFalcon/memmap2-rs This is a fork of the original memmap crate which appears to be unmaintained: https://github.com/danburkert/memmap-rs/issues/90 This fork is the most popular according to https://crates.io/keywords/mmap Differential Revision: https://phab.mercurial-scm.org/D11397

rust: Make OwningDirstateMap generic and move it into hg-core This will enable using it in rhg too. The `OwningDirstateMap::new_empty` constructor is generic and accepts a value of any type that gives acces to a bytes buffer. That buffer must stay valid as long as the value hasn’t been dropped, and must keep its memory address even if the value is moved. The `StableDeref` marker trait encodes those constraints. Previously no trait was needed because the value was always of type `PyBytes` which we know satisfies those constraints. The buffer type is ereased in the struct itself through boxing and dynamic dispatch, in order to simplify other signatures that mention `OwningDirstateMap`. Differential Revision: https://phab.mercurial-scm.org/D11396

rust: Move PyBytesWithData out of copy-tracing code So we can use it in other places to. Replace its `.data()` method with the `Deref<Target = [u8]>` trait, allowing this type to be used in generic contexts. Rename the type accordingly. Differential Revision: https://phab.mercurial-scm.org/D11395