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

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