Parameterize run-timeout coverage across benchmark lifecycle stages

[viraatc]

Context

PR #409 adds integration coverage for settings.timeouts.run_timeout_s during service launch, live performance, and metrics drain. Coverage is not yet organized as one sharp lifecycle-stage matrix equivalent to the SIGINT integration coverage.

Keep this as a test-focused follow-up rather than expanding PR #409 further. That PR is already approximately 1,510 non-test changed lines against the 1,300-line review target; this work would not add production behavior, but it would increase an already large review.

Lifecycle matrix

Parameterize the same run-watchdog contract across:

1. Service startup.
2. Endpoint-worker startup/connect.
3. Live session execution.
4. In-flight response drain.
5. Metrics tokenization drain.

Accuracy scoring/finalization is intentionally excluded and tracked separately in #464.

Acceptance criteria

• Each stage deterministically blocks at a known lifecycle boundary before the watchdog fires.
• Every case surfaces ExecutionError attributed to the run timeout.
• No case yields a complete: true run-level report.
• Child services and endpoint workers are not leaked.
• Overlapping one-off timeout tests are removed or folded into the parameterized matrix.
• Test synchronization uses observable stage boundaries rather than arbitrary sleeps.
• No production timeout behavior changes.