Function validate_aliases_inner 

pub fn validate_aliases_inner(
    problem_names: &BTreeMap<String, Vec<String>>,
    entries: &[(String, &[&str])],
) -> Result<(), Vec<String>>

Core validation logic, separated for testability with mock data.

• problem_names: lowercase key → list of human-readable sources (canonical names + problem-level aliases).
• entries: (variant_label, aliases_slice) per variant entry.