Function extract_call_edges 

pub fn extract_call_edges(
    parse_results: &[ParseResult],
    _resolver: &NameResolver,
    source_texts: &HashMap<String, String>,
    crate_dir: Option<&Path>,
) -> Vec<CodeEdge>

Extract call edges, preferring SCIP data when available.

When crate_dir is Some, this first attempts extract_scip_call_edges (which uses rust-analyzer for compiler-quality call detection). If rust-analyzer is unavailable or fails, falls back to text-scanning via text_scan_call_edges.

Pass crate_dir: None to always use text scanning (e.g. for Python).