clifecycle: add SetStopTimeout to make the shutdown grace period configurable

[ironAtom]

Summary

Lifecycle.Stop waits defaultStopTimeout (a hardcoded 30s) for background goroutines before running cleanup funcs and canceling the lifecycle context. Apps whose background work is bounded by a deadline of similar length (e.g. a job runner whose per-job timeout is also 30s) have zero margin: work claimed just before shutdown can be force-quit right as it is about to finish.

This adds Lifecycle.SetStopTimeout(d time.Duration) so apps can raise the grace period above their own work deadline. Default behavior is unchanged.

Test plan

• go build ./clifecycle/... and go vet ./clifecycle/... pass
• No behavior change unless the setter is called

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