rust-pyo3-dirstate: making bytes slices in core Sync For the purposes of providing PyO3 bindings, the data fields that will be exposed to Python have to be `Sync`, hence that is the case of `OwningDirstateMap` and its `owner` field. We had to do something similar for the PyO3 bindings of `revlog`. In this case, it forces us to adapt the `Deref` wrapper of `PyBytes` used in `hg-cpython`, because it must itself now be `Sync` and raw pointers are not. This looks even uglier than it used to, but it does not matter much, because our ultimate goal is to remove the rust-cpython bindings altogether.