dirstate: Removed unused instances of `DirsMultiset` … in Rust-backed dirstatemap. The Python class `dirstatemap` had cached properties `_dirs` and `_alldirs` that were not used for `hastrackeddir` and `hasdir` since they were redundant with corresponding fields for the Rust `DirstateMap` struct. `dirfoldmap` is modified to reuse instead the directory iterator introduced in 3b9914b28133c0918186b6e8b9e4f1916e21338d. Differential Revision: https://phab.mercurial-scm.org/D10921

dirstate-v2: Use 32-bit integers instead of 64-bit for offsets This saves 12 bytes per node. (Nodes representing files or directories.) These are offsets to other parts of the file. This would only be a limitation for a `.hg/dirstate` file larger than 4 GiB, which would only happen for a repository with dozens of millions of files and directories. Differential Revision: https://phab.mercurial-scm.org/D10920