[generate] shape checks in tests compatible with fixed-length caches (+ some minor fixes) (#35993)

* shape checks compatible with static cache

* add test

* tmp

* manually turn on eager attn when we want to output attn

* typo

* generalize to encoder-decoder models

* force compilation on cpu

* tmp commit

* fix static cache shape checks

* models with odd caches

* fix copies

* shorter cache search loop

* use decoder_past_key_values everywhere

* better test variable names and comments

* signature

* rename _check_outputs into _check_generate_outputs

* add comments

* HybridCache future test note

tests/models/recurrent_gemma/test_modeling_recurrent_gemma.py

@@ -367,9 +367,6 @@ class RecurrentGemmaModelTest(ModelTesterMixin, GenerationTesterMixin, PipelineT
     def test_training_gradient_checkpointing_use_reentrant_false(self):
         pass
 
-    def _check_attentions_for_generate(self, *args, **kwargs):
-        return True  # Model does not return attention
-
     @unittest.skip(reason="Past key values are not returned")
     def test_prompt_lookup_decoding_matches_greedy_search(self):
         pass
@@ -382,9 +379,6 @@ class RecurrentGemmaModelTest(ModelTesterMixin, GenerationTesterMixin, PipelineT
     def test_model_parallel_beam_search(self):
         pass
 
-    def _check_past_key_values_for_generate(self, *args, **kwargs):
-        return True
-
     @unittest.skip(reason="Rely on `past_key_values` to crop the assistant pkv. Not supported")
     def test_assisted_decoding_matches_greedy_search(self):
         pass
@@ -397,25 +391,6 @@ class RecurrentGemmaModelTest(ModelTesterMixin, GenerationTesterMixin, PipelineT
     def test_assisted_decoding_sample(self):
         pass
 
-    def _check_hidden_states_for_generate(
-        self, batch_size, hidden_states, min_length, max_length, config, use_cache=False, num_beam_groups=1
-    ):
-        self.assertIsInstance(hidden_states, tuple)
-        self.assertListEqual(
-            [isinstance(iter_hidden_states, tuple) for iter_hidden_states in hidden_states],
-            [True] * len(hidden_states),
-        )
-        self.assertEqual(len(hidden_states), (max_length - min_length) * num_beam_groups)
-
-        for idx, iter_hidden_states in enumerate(hidden_states):
-            seq_len = min_length + idx if not use_cache else 1
-            expected_shape = (batch_size * num_beam_groups, seq_len, config.hidden_size)
-            # check hidden size
-            self.assertListEqual(
-                [layer_hidden_states.shape for layer_hidden_states in iter_hidden_states],
-                [expected_shape] * len(iter_hidden_states),
-            )
-
     @unittest.skip(reason="TODO @arthurzucker not super important and failing.")
     def test_initialization(self):
         pass