Which issue or RFC does this PR close?

Related to #2457 and #2469; addresses their OceanBase acceptance timeouts independently of the SeekDB sharding fix in #2458.

Rationale for this change

Full Server initialization, migration checks and fixture cleanup share a 180-second process deadline. In #2457, the concurrent-startup case reported PASSED but was terminated before cleanup completed; its database drop finished shortly after the deadline. Other successful grant-migration cases already spent 130–144 seconds in the test body, plus cleanup and process startup.

What changes are included in this PR?

• Add a positive --test-timeout option to the isolated acceptance runner, defaulting to 180 seconds. Collection retains its separate 180-second deadline.
• Use 300 seconds for OceanBase clean migration, background lifecycle, concurrent startup and long-query cases. Scope-search and existing SeekDB calls retain their defaults.
• Increase the clean-migration step to 90 minutes and background lifecycle to 10 minutes. Startup and long-query steps retain 15 and 30 minutes. The job gets 180 minutes: 155 minutes of test-step budgets plus 25 minutes for setup, diagnostics and uploads.
• Preserve fail-on-timeout, complete JUnit validation, no skips and no retries, including when assertions pass before cleanup times out.

Are there any user-facing changes?

CI execution budgets only. No runtime, API or database-format changes.

How was this change tested?

• New CLI and cleanup-deadline regressions failed before implementation. Real subprocess tests exercise GNU timeout with synthetic pytest cases, including collection independence and cleanup timeout after PASSED.
• pytest tests/test_atomic_memory_migration_shards.py tests/test_check_atomic_memory_migration_shards.py tests/test_ci_changes.py tests/test_ci_pipeline.py -q: 171 passed. After increasing the synthetic timing margins, all 24 runner tests passed again.
• make check, uv run prek run -a, and git diff --check: passed.
• Actual OceanBase test collection confirms 47 clean-migration cases (at most 16 per shard), 1 background case, 3 startup cases and 8 long-query cases. Including collection and termination grace, the largest step needs at most 85.83 minutes within its 90-minute budget.
• Independent review found no blocking issues. Local validation covers runner behavior and budget calculations; real OceanBase execution remains a GitHub CI acceptance check.

AI usage statement

OpenAI Codex assisted with diagnosis, implementation, tests and independent review.