Clean up and fix test suites in CI

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.

Merged #6954 (af073e331, dev deploy green): fixed the order-dependent pool-tick statement-budget flake (settings TTL pin, mutation-proven), retired 5 stale tests. test.yml reds were already fixed; latest runs green. Speed levers measured, none taken. Memory: used mem-18424; proposed 1 gotcha.