refactor(rpiv-pi): share one settle-and-emit epilogue across lane teardown paths

Extract settleAndEmitCleared - the ordering-contract epilogue (capture parked
units before the settle, resolve every parked resolver with undefined, run the
site mutation, notify, then emit `cleared` for only the units that had parked
input) - out of the four teardown sites that each spelled it inline:
recordRun reactivation, retireRun, evictRun, and clearUnitLanes.

Pin the ordering with tests: notify precedes `cleared` per path, a fresh
recordRun notifies without emitting, and an empty clearUnitLanes does neither.