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

from __future__ import absolute_import
import os

if os.environ.get('COVERAGE_PROCESS_START'):
    try:
        import coverage
        import uuid

        covpath = os.path.join(
            os.environ['COVERAGE_DIR'], 'cov.%s' % uuid.uuid1()
        )
        cov = coverage.coverage(data_file=covpath, auto_data=True)
        cov._warn_no_data = False
        cov._warn_unimported_source = False
        cov.start()
    except ImportError:
        pass