Implement NIE_30 (event finish after step, teardown at scenario end)

Per #203, `NIE_30` is currently not implemented (only `NIE_23` and `NIE_33` are, see #197 and `ExecutionMode.NON_INTERRUPTIVE`'s `behaviorTypes` whitelist).

| Behavior | Event Start | Event Start Finish | Tear Down |
| - | - | - | - |
| NIE_30 | Before Step | After Step | latest scenario end |

Like `NIE_33`, the event does not need to finish before the following step runs, but unlike `NIE_33`, tear-down is deferred to the end of the scenario instead of happening right after the step.

See the shared behavior-code documentation in [README.md#non-interruptive-execution-mode](https://github.com/adobe/phased-testing/blob/main/README.md#non-interruptive-execution-mode) and [README.md#wrapping-an-event-around-a-step](https://github.com/adobe/phased-testing/blob/main/README.md#wrapping-an-event-around-a-step).

Start with the shared behavior-code sections in README.md, then inspect ExecutionMode.NON_INTERRUPTIVE and the existing NIE_23 and NIE_33 implementations. Compare their event timing and teardown handling, and verify that NIE_30 is recognized and behaves as documented: it starts before the step, finishes after the step, and tears down at the latest scenario end.

Written by the indexing model from the issue text.