def [](name, *traits, **attrs)
      registry[name].struct_namespace(struct_namespace).create(*traits, attrs)
    end
def [](name, *traits, **attrs)
      registry[name].struct_namespace(struct_namespace).create(*traits, attrs)
    end
@api private
 Build an in-memory struct

 @example create a struct with default attributes
   MyFactory[:user]

 @example create a struct with some attributes overridden
   MyFactory.structs[:user, name: "Jane"]

 @param [Symbol] name The name of the registered factory
 @param [Hash] attrs An optional hash with attributes

 @return [ROM::Struct]

 @api public