def method_missing(meth, *_args, &block)
      format = FormatRegistry.formats[meth]
      return unless format && format.match?(@route_handler.request)
      @candidates << format
      @blocks[meth] = block
    end
def method_missing(meth, *_args, &block)
      format = FormatRegistry.formats[meth]
      return unless format && format.match?(@route_handler.request)
      @candidates << format
      @blocks[meth] = block
    end
Creates a format handler for a route handler
 @param [Kawaii::RouteHandler] current route handler
 @return {FormatHandler}
 Matches method invoked in end-user code with {FormatBase#key}.
 If format matches the current request, it saves it for negotiation
 in {FormatHandler#response}.