models.py -> loaders/ module refactor (#2680)

* models.py -> loaders/ module refactor

* refactor ModelLoader class

* plugin manager changes

* circular import fix

* pytest

* pytest

* minor improvements

* fix

* minor changes

* fix test

* remove dead code

* coderabbit comments

* lint

* fix

* coderabbit suggestion I liked

* more coderabbit

* review comments, yak shaving

* lint

* updating in light of SP ctx manager changes

* review comment

* review comment 2

tests/patched/test_validation.py

@@ -9,11 +9,11 @@ from typing import Optional
 import pytest
 from pydantic import ValidationError
 
+from axolotl.loaders.utils import check_model_config
 from axolotl.utils import is_comet_available
 from axolotl.utils.config import validate_config
 from axolotl.utils.dict import DictDefault
 from axolotl.utils.mlflow_ import setup_mlflow_env_vars
-from axolotl.utils.models import check_model_config
 from axolotl.utils.schemas.config import AxolotlConfigWCapabilities
 from axolotl.utils.wandb_ import setup_wandb_env_vars
 
@@ -1215,6 +1215,20 @@ class TestValidation(BaseValidation):
             cfg, capabilities=capabilities, env_capabilities=env_capabilities
         )
 
+    def test_cfg_throws_error_with_s2_attention_and_sample_packing(self, minimal_cfg):
+        test_cfg = DictDefault(
+            {
+                "s2_attention": True,
+                "sample_packing": True,
+            }
+            | minimal_cfg
+        )
+        with pytest.raises(
+            ValidationError,
+            match=r".*shifted-sparse attention does not currently support sample packing*",
+        ):
+            validate_config(test_cfg)
+
 
 class TestTorchCompileValidation(BaseValidation):
     """