coverage: use ctrace core to avoid CI slowdown on Python 3.14

[bluetech]

While sysmon (default since Python 3.14) is supposed to be faster, it about 3x slower in CI (~24m vs. ~8m) ATM.

https://coverage.readthedocs.io/en/latest/config.html#config-run-core https://coverage.readthedocs.io/en/latest/faq.html#q-coverage-py-is-much-slower-than-i-remember-what-s-going-on

[webknjaz]

Have you reported this to @nedbat?

[bluetech]

There is already an issue coveragepy/coveragepy#2082.

[patchback]

Backport to 9.0.x: 💔 cherry-picking failed — conflicts found

❌ Failed to cleanly apply 1b5200c on top of patchback/backports/9.0.x/1b5200c0f056ec58f5620417d3157aea3ba33c87/pr-13991

Backporting merged PR #13991 into main

1. Ensure you have a local repo clone of your fork. Unless you cloned it
   from the upstream, this would be your origin remote.
2. Make sure you have an upstream repo added as a remote too. In these
   instructions you'll refer to it by the name upstream. If you don't
   have it, here's how you can add it:

   $ git remote add upstream https://github.com/pytest-dev/pytest.git

3. Ensure you have the latest copy of upstream and prepare a branch
   that will hold the backported code:

   $ git fetch upstream
   $ git checkout -b patchback/backports/9.0.x/1b5200c0f056ec58f5620417d3157aea3ba33c87/pr-13991 upstream/9.0.x

4. Now, cherry-pick PR coverage: use ctrace core to avoid CI slowdown on Python 3.14 #13991 contents into that branch:

   $ git cherry-pick -x 1b5200c0f056ec58f5620417d3157aea3ba33c87

   If it'll yell at you with something like fatal: Commit 1b5200c0f056ec58f5620417d3157aea3ba33c87 is a merge but no -m option was given., add -m 1 as follows instead:

   $ git cherry-pick -m1 -x 1b5200c0f056ec58f5620417d3157aea3ba33c87

5. At this point, you'll probably encounter some merge conflicts. You must
   resolve them in to preserve the patch from PR coverage: use ctrace core to avoid CI slowdown on Python 3.14 #13991 as close to the
   original as possible.
6. Push this branch to your fork on GitHub:

   $ git push origin patchback/backports/9.0.x/1b5200c0f056ec58f5620417d3157aea3ba33c87/pr-13991

7. Create a PR, ensure that the CI is green. If it's not — update it so that
   the tests and any other checks pass. This is it!
   Now relax and wait for the maintainers to process your pull request
   when they have some cycles to do reviews. Don't worry — they'll tell you if
   any improvements are necessary when the time comes!

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[nedbat]

It might be helpful to run the tests with sysmon, and also COVERAGE_SYSMON_LOG=1, then take a look at /tmp/foo.out. Other reports of the slowdown have been due (I think) to many duplicate code objects.

[nedbat]

And BTW, use the latest main of coveragepy to get full details.

[nicoddemus]

Backported manually: #13995