[Fuyu] Add tests (#27001)

* Add tests

* Add integration test

* More improvements

* Fix tests

* Fix style

* Skip gradient checkpointing tests

* Update script

* Remove scripts

* Remove Fuyu from auto mapping

* Fix integration test

* More improvements

* Remove file

* Add Fuyu to slow documentation tests

* Address comments

* Clarify comment

utils/slow_documentation_tests.txt

@@ -6,4 +6,5 @@ docs/source/en/task_summary.md
 docs/source/en/tasks/prompting.md
 src/transformers/models/blip_2/modeling_blip_2.py
 src/transformers/models/ctrl/modeling_ctrl.py
-src/transformers/models/kosmos2/modeling_kosmos2.py
+src/transformers/models/fuyu/modeling_fuyu.py
+src/transformers/models/kosmos2/modeling_kosmos2.py