add validation around cce + chunked_ce (#2932) [skip ci]

* add validation around cce + chunked_ce

* return on end of validation method

src/axolotl/integrations/cut_cross_entropy/args.py

@@ -41,3 +41,13 @@ class CutCrossEntropyArgs(BaseModel):
             )
 
         return data
+
+    @model_validator(mode="before")
+    @classmethod
+    def check_chunked_cross_entropy_not_set(cls, data):
+        if data.get("chunked_cross_entropy"):
+            raise ValueError(
+                "Cut Cross Entropy does not support chunked cross entropy. "
+                "Please set `chunked_cross_entropy` to `False` or disable Cut Cross Entropy."
+            )
+        return data