Problem

I spent a few minutes seeing how fast I could get our regression test suite to run on my workstation, for when I want to run a "did I break anything?" smoke test before pushing to CI.

• Test runtime was dominated by a couple of tests that run for longer than all the others take together
• Test concurrency was limited to <16 by the ports-per-worker setting

There's no "right answer" for how long a test should
be, but as a rule of thumb, no one test should run
for much longer than the time it takes to run all the
other tests together.

Summary of changes

• Make the ports per worker setting dynamic depending on worker count
• Modify the longest running tests to run for a shorter time (test_duplicate_layers which uses a pgbench runtime) or fewer iterations (test_restarts_frequent_checkpoints).

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist