fn append_used_wrapper_helpers(content: &mut String, fragments: &[Cow<'_, str>])Expand description
Emit an optional preamble helper only when a collected fragment names it.
A name in a roxygen comment also keeps its helper, which is harmless.
The one dependency between optional helpers is explicit:
.miniextendr_caller_call raises through .miniextendr_arg_error. The
helpers every preamble has (condition transport, the frame resolver, the
conversion-error class) are written unconditionally.