Refactor subgroup checks and simplify ritual additional hooks

[vuryleo]

Summary

• refactor subgroup recursive selection/check logic and same-layer dedupe around subgroup contexts and check specs
• simplify ritual additional-hook handling and align custom ATK-based ritual checks with the same subgroup/classifier model
• migrate card-script subgroup call sites to the new chain syntax and keep the branch aligned with origin/patch-gcheck-classifier

API changes

• GCheckAdditional now receives only the current subgroup; utility-side subgroup checks no longer pass the selected card or branch pool
• RGCheckAdditional now receives only the current ritual material subgroup; ritual-side additional checks no longer pass a singled-out material
• distinct-check helpers are exposed as *_check plus *_check_spec pairs (for example dncheck / dncheck_spec), and the older exported *_additional / *_classifier helpers are removed from the utility surface
• subgroup classifiers are now treated as classifier(c) values and are precomputed once per subgroup context
• subgroup contexts now also have chain syntax sugar on Group, e.g. g:WithSubGroupContext(additional, classifier):CheckSubGroup(...) and g:WithCheckSpec(spec):SelectSubGroup(...)

Notes

• includes merge/resolution commits needed to integrate origin/patch-gcheck-classifier and follow-up local fixes
• touched ritual helper cards and subgroup-helper card scripts were updated to match the subgroup-only hook contract and the new chain-style subgroup API

[purerosefallen]

I don't suggest introducing breaking changes to GCheckAdditional
it's ok to change GCheckClassifier signature because it's WIP