rust-index: remove one collect when converting back Turns out this is slightly faster. Sending the results back to Python is still the most costly (like 75% of the time) of the whole method, but it's about as fast as it can be now. hg perf::phases on mozilla-try-2023-03-22 before: 0.267114 after: 0.247101

To run the tests, do:

cd tests/
python run-tests.py

See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.