The eowyn.sh script is used in a github workflow, but after
commit 0d56ba3 (build: restore the exercise chain), the github action
will take more time to complete.
Enable full build parallelism, when -Dhealed is true and -Dn is null.
Use the standard CompileStep and RunStep, instead of ZiglingStep.
On my PC, this change reduces the build time by about 30%.