checkpoint model on first step callback (#2906)

* checkpoint model on first step callback

* remove debug

* add test cases; update existing tests not to save on first step

* move test out of solo

* delete

* default to False

* typo

tests/e2e/solo/test_flex.py

@@ -49,6 +49,7 @@ class TestPackedFlex(unittest.TestCase):
                 "lr_scheduler": "cosine",
                 "max_steps": 5,
                 "use_tensorboard": True,
+                "save_first_step": False,
             }
         )
         if is_torch_bf16_gpu_available():