world_spawn starts a vanilla and a Horizon server for each of 60 seeds,
one at a time: 1,144-1,548 s on the CI runner, the parity job's longest
harness and its floor whenever a PR's changes reach it. With
PARITY_SHARDS = 4 each shard creates every fourth seed's worlds, in its
own build directory.
The shard helper datafix had moves to tools/parity_shard.py, which both
use. It stays out of lab.py, which every harness imports.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Ludovic Marie