save_factors parameter no longer functional in v2.0.2

[chmnsk]

Bug

The save_factors parameter, which was functional in version v2.0.1, seems to have no effect in the recent v2.0.2 release.

To Reproduce

Steps to reproduce the behavior:

1. Set up the environment with v2.0.2
2. Set save_factors from als_option as True in

   buffalo/examples/example_als.py

   Lines 10 to 25 in f44127b

   	def example1():
   	log.set_log_level(log.DEBUG)
   	als_option = ALSOption().get_default_option()
   	als_option.validation = aux.Option({"topk": 10})
   	data_option = MatrixMarketOptions().get_default_option()
   	data_option.input.main = "../tests/ext/ml-100k/main"
   	data_option.input.iid = "../tests/ext/ml-100k/iid"
   	als = ALS(als_option, data_opt=data_option)
   	als.initialize()
   	als.train()
   	print("MovieLens 100k metrics for validations\n%s" % json.dumps(als.get_validation_results(), indent=2))
   	print("Similar movies to Star_Wars_(1977)")
   	for rank, (movie_name, score) in enumerate(als.most_similar("49.Star_Wars_(1977)")):
   	print(f"{rank + 1:02d}. {score:.3f} {movie_name}")

3. Observe that the ALS model is not saved during training, whereas in v2.0.1 it was working as expected.