rhg: Update the dirstate on disk after status Differential Revision: https://phab.mercurial-scm.org/D11840

rhg: Add Repo::write_dirstate This method is not used yet. It saves to disk any mutation that was done to the `Repo`’s dirstate through `Repo::dirstate_map_mut`. It takes care of dirstate-v1 v.s. dirstate-v2, dockets, data files, appending when possible, etc. Differential Revision: https://phab.mercurial-scm.org/D11839

rhg: Add lazy/cached dirstate data file ID parsing on Repo The `dirstate_parents`, `dirstate_data_file_uuid`, and `dirstate_map` members of `Repo` can be access in any order and the `.hg/dirstate` file should only be opened once. Differential Revision: https://phab.mercurial-scm.org/D11838

rhg: Make Repo::dirstate_parents a LazyCell Unify with the same abstraction used for other lazily-initialized components Differential Revision: https://phab.mercurial-scm.org/D11837

rust: Add Vfs::write_atomic This method writes to a temporary file then renames in place Differential Revision: https://phab.mercurial-scm.org/D11836

rhg: Initial repository locking Initial Rust implementation of locking based on the `.hg/wlock` symlink (or file), with lock breaking when the recorded pid and hostname show that a lock was left by a local process that is not running anymore (as it might have been killed). Differential Revision: https://phab.mercurial-scm.org/D11835

rust: Serializing a DirstateMap does not mutate it anymore Differential Revision: https://phab.mercurial-scm.org/D11834