Function emit_nested_call 

fn emit_nested_call(
    call: &LowerCall,
    scope_lets: &mut Vec<TokenStream>,
) -> TokenStream

Emit a nested call expression (returns the SEXP, adds protect_raw lines to the parent scope via a temporary).

For namespaced nested calls (pkg::fn(args…)), the namespace resolution is inlined via RCall::namespaced(pkg, fun)?.build(). The ? propagates resolution errors to the outer Result<SEXP, String> return.