Function validate_unused_kinds_audit 

pub fn validate_unused_kinds_audit(
    lang: &dyn Language,
    documented_unused: &[&str],
) -> Result<(), String>

Validate that a language’s unused node kinds audit is complete and accurate.

This function checks:

1. All kinds in documented_unused actually exist in the grammar
2. All potentially useful kinds from the grammar are either used or documented

Call this from each language’s unused_node_kinds_audit test.