workspace-test nightly: widen the tests lane from aprender-core to the workspace after one measured run #5027

Refs #5002. Owner aprender-a7n.

#5002's nightly runs CI's quick-tier line cargo nextest run --profile ci --lib --tests$pkgs as its tests lane, with $pkgs bound to -p aprender-core (quorum q-5002d, Q1 KT: the crate #5002 names now, the workspace after one measured run). The full-tier lib line is --lib only, so the integration targets of every other crate still get no run on main's head.

done_when: one dispatch of the nightly with the tests lane at --workspace --exclude aprender-gpu --exclude aprender-cuda-edge --exclude aprender-compute (the full-tier lib line's exclusions) is measured: its time, and each red sorted as a tree red (one ticket each) or a host-only red. Then a PR widens TESTS_PKGS and cites that run id, or this ticket records why not.

Blocked by #5002 merging.