Function build_r_call_args_from_sig 

pub(crate) fn build_r_call_args_from_sig(
    sig: &Signature,
    formals: &Formals,
    absent_formals: HashMap<String, String>,
) -> String

Build R .Call() arguments from a Rust function signature.

Automatically skips self/&self receivers (those are passed separately via DotCallBuilder::with_self). &Dots becomes list(...), LazyDots environment(). absent_formals are the choice parameters that read a value identical() to their formal as omitted (see RArgumentBuilder::with_absent_formals).

Returns a comma-separated string of R call arguments, e.g., "x, y, list(...)". formals names each parameter, as in build_r_formals_from_sig.