Fix and prune GitHub Actions tests

Review all test suites, delete stale, superseeded, those that were one off to check feature flags or absence of something. Kill the most long running or flaky with unit tests that execute in milliseconds. Regroup between quick and full, Fix broken tests in CI - GitHub Actions - look at a few recent test runs and fix broken/flaky tests. Babysit CI/CD until the tests (test.yaml) pass.

Fixed 2 live CI flakes (proven by induction), pruned 3 one-off tests; other CI reds were already fixed upstream. PR #4715 merged, full gate + Jaah Deploy green. Deferred: unreproduced fixture_db worker crash.