[TO BE MERGED AROUND NOVEMBER] Make safetensors the default #3291

Job	Run time
run-tests (latest, test_prod)	2m 19s
run-tests (latest, test_core)	3m 2s
run-tests (latest, test_cli)	6m 40s
run-tests (latest, test_big_modeling)	3m 34s
run-tests (latest, test_deepspeed)	1m 28s
run-tests (latest, test_fsdp)	4m 13s
run-tests (latest, test_example_differences)	1m 20s
run-tests (latest, test_checkpoint_step)	4m 17s
run-tests (latest, test_checkpoint_epoch)	4m 6s
run-tests (latest, test_rest)	14m 30s
run-tests (minimum, test_prod)	2m 11s
run-tests (minimum, test_core)	3m 34s
run-tests (minimum, test_cli)	5m 35s
run-tests (minimum, test_big_modeling)	3m 14s
run-tests (minimum, test_deepspeed)	1m 9s
run-tests (minimum, test_fsdp)	1m 34s
run-tests (minimum, test_example_differences)	1m 28s
run-tests (minimum, test_checkpoint_step)	3m 32s
run-tests (minimum, test_checkpoint_epoch)	3m 55s
run-tests (minimum, test_rest)	15m 39s
	1h 27m 20s

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