Sample execution timeout clocks adaptively (GOL-512)

[noise64]

• addresses GOL-512\n- samples the timeout clock at an adaptive QuickJS interrupt stride targeting 10% of the configured timeout, while checking cancellation on every interrupt\n- documents best-effort timeout behavior and covers the sampler with three deterministic unit tests plus the existing normal-feature execution integration test\n- focused local P2/P3 execution tests pass; user reports a successful manual Golem smoke test\n- detailed Golem oplog counts, replay behavior, and unrelated-worker impact remain to be validated separately; keep GOL-512 open