add smart-reply function
the idea is to free the user from having to decide which reply function to use when the message itself already suggests the correct default action.
said smart-reply function would first try a list reply, and when no lists are found, fall back to group-reply (so an obvious alternative name would be list-group-reply, but that seems unnecessarily convoluted and open to misinterpretation). related discussion can be found at https://marc.info/?l=mutt-dev&m=104039412814956&w=2 ff. (though the archive is clearly missing some mails; also, the thread goes way off-topic towards the end).
an alternative implementation of smart-reply would be to make it always group-reply, but exclude the sender if any mailing lists are across the recipients - this should be functionally equivalent to the above if list-reply and group-reply are implemented coherently.
in either case, the mail-followup-to header should be heeded with highest priority if present. this is something a combined "smart" function can do much more cleanly than separate functions with narrow contracts that (partially) contradict the header's meaning.