A run that a signal ends has a null exit code, so the runner recorded a
pass when Node and the executable ended by different signals, or when one
ended by a signal and the other with an exit code compared as null. The
verdict now compares both the exit code and the signal (verdict.mjs), and
records Node's signal in nodeExit as it does for the executable.
A relative --node path also made the minimal lane's fixtures symlink
relative to the copied tree, where it does not resolve. The checkout path
is now resolved first.
tests/harness/node-parallel-runner.test.ts covers both: the termination
comparison, and a relative --node path whose fixtures resolve from the
minimal tree.
