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/patched/test_model_patches.py

@@ -45,6 +45,7 @@ class TestModelPatches(unittest.TestCase):
                 "max_steps": 20,
                 "save_steps": 10,
                 "eval_steps": 10,
+                "save_first_step": False,
             }
         )
         cfg = validate_config(cfg)
@@ -78,6 +79,7 @@ class TestModelPatches(unittest.TestCase):
                 "max_steps": 20,
                 "save_steps": 10,
                 "eval_steps": 10,
+                "save_first_step": False,
             }
         )
         cfg = validate_config(cfg)