Trainer callbacks (#7596)

* Initial callback proposal

* Finish various callbacks

* Post-rebase conflicts

* Fix tests

* Don't use something that's not set

* Documentation

* Remove unwanted print.

* Document all models can work

* Add tests + small fixes

* Update docs/source/internal/trainer_utils.rst

Co-authored-by: Lysandre Debut <lysandre@huggingface.co>

* Address review comments

* Fix TF tests

* Real fix this time

* This one should work

* Fix typo

* Really fix typo

Co-authored-by: Lysandre Debut <lysandre@huggingface.co>

src/transformers/utils/dummy_pt_objects.py

@@ -1869,19 +1869,10 @@ class MarianTokenizer:
         requires_pytorch(self)
 
 
-class EvalPrediction:
-    def __init__(self, *args, **kwargs):
-        requires_pytorch(self)
-
-
 class Trainer:
     def __init__(self, *args, **kwargs):
         requires_pytorch(self)
 
 
-def set_seed(*args, **kwargs):
-    requires_pytorch(set_seed)
-
-
 def torch_distributed_zero_first(*args, **kwargs):
     requires_pytorch(torch_distributed_zero_first)