Function is_data_language 

pub fn is_data_language(lang: &str) -> bool

Returns true for “data” languages: specs whose import_query and call_query are both empty (JSON and YAML).

Such files carry no import/call-graph structure, only per-key property symbols, so an oversized one can be indexed content-only without losing any graph signal. Driven by the spec rather than a hard-coded extension list, so future data languages are covered automatically (gobby-cli #678).