rust-dirstatemap: add missing @propertycache While investigating a regression on `hg update` performance introduced by the Rust `dirstatemap`, two missing `@propertycache` were identified when comparing against the Python implementation. This adds back the first one, that has no observable impact on behavior. The second one (`nonnormalset`) is going to be more involved, as the caching has to be done from the Rust side of things. Differential Revision: https://phab.mercurial-scm.org/D8047

#require black

  $ cd $RUNTESTDIR/..
  $ black --config=black.toml --check --diff `hg files 'set:(**.py + grep("^#!.*python")) - mercurial/thirdparty/** - "contrib/python-zstandard/**"'`