Review and fix test suites and CI failures

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 6 CI flakes at cause (incl. idempotency heartbeat product bug), added worker-crash faulthandler dump, deleted 2 stale tests; test.yml green twice on branch, PR #7872 merged a8de438, deploy green. SIGSEGV trigger still open (diagnostic now in place). Memory: none applied.