rust-dirstatemap: use `get_node_mut` instead or `get_or_insert_node` This (along with the docstring), makes it more obvious that we're not expecting to insert a node here. This is less prone to bugs in later refactorings. Differential Revision: https://phab.mercurial-scm.org/D12530

rust-dirstatemap: add `each_ancestor` argument to `get_node_mut` This forces the callers to think about if the counters in the ancestors need to be adjusted. Differential Revision: https://phab.mercurial-scm.org/D12529

rust-dirstatemap: add simpler method `get_or_insert_node` for the common case All but one case use the exact same input for most arguments, this simplifies code and reduces footgun potential. Differential Revision: https://phab.mercurial-scm.org/D12528

rust-dirstatemap: inline the last `get_or_insert` call The `get_or_insert` method was dangerous because it did not take the `DirstateMap` counters into account. This particular instance does not need to update the counters. Differential Revision: https://phab.mercurial-scm.org/D12527

rust-dirstatemap: add `set_cached_mtime` helper method This will help remove the `get_or_insert` method, which is dangerous because it does not take the `DirstateMap` counters into account Differential Revision: https://phab.mercurial-scm.org/D12526

rust-dirstatemap: add `clear_cached_mtime` helper method This will help remove the `get_or_insert` method, which is dangerous because it does not take the `DirstateMap` counters into account. Differential Revision: https://phab.mercurial-scm.org/D12525

rust-dirstatemap: add unit tests These were missing and have already proven valuable since they have found two bugs (fixed in previous patches). There may be other behavior to test, but this gives us a decent coverage. Differential Revision: https://phab.mercurial-scm.org/D12524

rust: add `Debug` trait to a bunch of structs This is useful when... debugging. Right now the output is not in the most readable state it could be, but this is very low effort and is good enough for now. We may want to write a nicer custom debug formatter for some of those structs in the future. Differential Revision: https://phab.mercurial-scm.org/D12523

rust-dirstatemap: use `&HgPath` instead of `HgPathBuf` in `copy_map_insert` No reason to require an owned path here. Differential Revision: https://phab.mercurial-scm.org/D12522

rust-dirstatemap: use `DirstateEntry::tracked` directly `state()` is a legacy API that will be removed at some point, let's use the newer API. Differential Revision: https://phab.mercurial-scm.org/D12521