By: Tom Sydney Kerckhove <syd@cs-syd.eu>
Consolidate mutation settings into Maybe MutationSettings sum type Replace the 14 flat settingMutation* fields on Settings with a single settingMutation :: Maybe MutationSettings, where MutationSettings carries a mutationMode sum that selects one of four sub-records (coverage parent, coverage child, mutation parent, mutation child). This makes mutation mode invariants type-level: the child-only options (output file, baseline file) sit on the child record, the parent-only options (report dir, suite exes, child mem limit, jobs, retry) sit on the parent records, and exhaustiveness checking now catches missing modes in the dispatcher.