dirstate-v2: Drop parent directory cache when removing a dirstate node The premise of the directory cache is that the dirstate contains child nodes for every entry that `read_dir` would return. When removing nodes, that may not be the case anymore so the cache should be invalidated. Differential Revision: https://phab.mercurial-scm.org/D10829

dirstate-v2: Add --dirs to debugdirstate command `hg debugdirstate --dirs` also shows information stored in the dirstate (for `read_dir` caching) about directories. Differential Revision: https://phab.mercurial-scm.org/D10828

dirstate-v2: Write .hg/dirstate back to disk on directory cache changes Differential Revision: https://phab.mercurial-scm.org/D10827

dirstate-v2: Skip readdir in status based on directory mtime When calling `read_dir` during `status` and the directory is found to be eligible for caching (see code comments), write the directory’s mtime to the dirstate. The presence of a directory mtime in the dirstate is meaningful and indicates eligibility. When an eligible directory mtime is found in the dirstate and `stat()` shows that the mtime has not changed, `status` can skip calling `read_dir` again and instead rely on the names of child nodes in the dirstate tree. The `tempfile` crate is used to create a temporary file in order to use its modification time as "current time" with the same truncation as other files and directories would have in their own modification time. Differential Revision: https://phab.mercurial-scm.org/D10826

dirstate-v2: Allow tree nodes without an entry to store a timestamp Timestamps are stored on 96 bits: * 64 bits for the signed number of seconds since the Unix epoch * 32 bits for the nanoseconds in the `0 <= ns < 1_000_000_000` range For now timestamps are not used or set yet. Differential Revision: https://phab.mercurial-scm.org/D10825

dirstate-tree: Change status() results to not borrow DirstateMap The `status` function takes a `&'tree mut DirstateMap<'on_disk>` parameter. `'on_disk` borrows a read-only byte buffer with the contents of the `.hg/dirstate` file. `DirstateMap` internally uses represents file paths as `std::borrow::Cow<'on_disk, HgPath>`, which borrows the byte buffer when possible and allocates an owned string if not, such as for files added to the dirstate after it was loaded from disk. Previously the return type of of `status` has a `'tree` lifetime, meaning it could borrow all paths from the `DirstateMap`. With this changeset, that lifetime is changed to `'on_disk` meaning that only paths from the byte buffer can be borrowed, and paths allocated by `DirstateMap` must be copied. Usually most paths are in the byte buffer, and most paths are not part of the return value of `status`, so the number of extra copies should be small. This change will enable `status` to mutate the `DirstateMap` after it has finished constructing its return value. Previously such mutation would be prevented by possible on-going borrows. Differential Revision: https://phab.mercurial-scm.org/D10824

dirstate-tree: Fix status algorithm with unreadable directory When reading a directory fails such as because of insufficient permissions, it should be treated as empty by status instead of skipped entirely. Differential Revision: https://phab.mercurial-scm.org/D10823