chore: add performance regression test infrastructure.

#4072 shows that performance can be seriously impacted by small changes.

Today, with our CI, we would not detect any serious performance regression.

Goal: add some performance regression test infrastructure, in Github Actions, Jenkins or elsewhere if appropriate.

Start by reviewing issue #4072 and the repository's current CI configuration. Define how performance regressions should be measured and detected, then choose an appropriate CI system; the work is done when the infrastructure reliably flags serious performance regressions.

Written by the indexing model from the issue text.