Release update 20250331 (#2460) [skip ci]

* make torch 2.6.0 the default image

* fix tests against upstream main

* fix attribute access

* use fixture dataset

* fix dataset load

* correct the fixtures + tests

* more fixtures

* add accidentally removed shakespeare fixture

* fix conversion from unittest to pytest class

* nightly main ci caches

* build 12.6.3 cuda base image

* override for fix from huggingface/transformers#37162

* address PR feedback

.github/workflows/tests.yml

@@ -96,6 +96,10 @@ jobs:
         run: |
           axolotl --help
 
+      - name: Pre-Download dataset fixture
+        run: |
+          huggingface-cli download --repo-type=dataset axolotl-ai-internal/axolotl-oss-dataset-fixtures
+
       - name: Run tests
         run: |
           pytest -v -n8 --dist loadfile --ignore=tests/e2e/ --ignore=tests/patched/ --ignore=tests/cli/ tests/