Function method_source_tag 

pub(crate) fn method_source_tag(
    type_ident: &Ident,
    method_ident: &Ident,
) -> String

Build a roxygen @source traceability line for a class method.

Returns "#' @source Generated by miniextendr from \Type::method`“. Use this wherever a class-generator needs to emit a source-provenance comment linking the generated R wrapper back to the originating Rust impl` block method.