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
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).