The nursery goes default-on

After a two-week pause, the non-moving generational nursery is enabled by default, taking the headline capture from 1.283× to 1.212× Node.

The log had been quiet since 4 August. 74d03d23 is "the nursery goes default-on": minor collections trace young reachability plus remembered old-to-young edges; promotion is a bookkeeping change on the same heap index because the collector never moves objects. The wave-9 capture moved from 1.2832× to 1.2117×. ZIPP_NO_NURSERY=1 keeps the majors-only mode for conformance runs and ablations.