narrowspec: add timing block for validating narrowspec
This was showing up in an operation I was doing today, and I'd like to
be able to get trace spans for it instead of just profiler samples.
Differential Revision: https://phab.mercurial-scm.org/D12185
#require rustfmt test-repo
$ . "$TESTDIR/helpers-testrepo.sh"
$ cd "$TESTDIR"/..
Warning: Keep this in sync with hghave.py
$ RUSTFMT=$(rustup which --toolchain nightly-2021-11-02 rustfmt)
$ for f in `testrepohg files 'glob:**/*.rs'` ; do
> $RUSTFMT --check --edition=2018 --unstable-features --color=never $f
> done