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 docutils gettext

  $ $TESTDIR/check-gendoc de
  checking for parse errors
  Die Dateien werden dem Projektarchiv beim n\xc3\xa4chsten \xc3\x9cbernehmen (commit) hinzugef\xc3\xbcgt. Um dies vorher r\xc3\xbcckg\xc3\xa4ngig zu machen, siehe:hg:`forget`. (esc)
  warning: please have a space before :hg: