Add Watermarking LogitsProcessor and WatermarkDetector (#29676)

* add watermarking processor

* remove the other hashing (context width=1 always)

* make style

* Update src/transformers/generation/logits_process.py

Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>

* Update src/transformers/generation/logits_process.py

Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>

* Update src/transformers/generation/logits_process.py

Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>

* Update src/transformers/generation/configuration_utils.py

Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>

* update watermarking process

* add detector

* update tests to use detector

* fix failing tests

* rename `input_seq`

* make style

* doc for processor

* minor fixes

* docs

* make quality

* Update src/transformers/generation/configuration_utils.py

Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>

* Update src/transformers/generation/logits_process.py

Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>

* Update src/transformers/generation/watermarking.py

Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>

* Update src/transformers/generation/watermarking.py

Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>

* Update src/transformers/generation/watermarking.py

Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>

* add PR suggestions

* let's use lru_cache's default max size (128)

* import processor if torch available

* maybe like this

* lets move the config to torch independet file

* add docs

* tiny docs fix to make the test happy

* Update src/transformers/generation/configuration_utils.py

Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>

* Update src/transformers/generation/watermarking.py

Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>

* PR suggestions

* add docs

* fix test

* fix docs

* address pr comments

* style

* Revert "style"

This reverts commit 7f33cc34ff08b414f8e7f90060889877606b43b2.

* correct style

* make doctest green

---------

Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>

docs/source/en/internal/generation_utils.md

@@ -209,6 +209,10 @@ generation.
 [[autodoc]] WhisperTimeStampLogitsProcessor
     - __call__
 
+[[autodoc]] WatermarkLogitsProcessor
+    - __call__
+
+
 ### TensorFlow
 
 [[autodoc]] TFForcedBOSTokenLogitsProcessor
@@ -372,3 +376,10 @@ A [`Constraint`] can be used to force the generation to include specific tokens
     - update
     - get_seq_length
     - reorder_cache
+
+
+## Watermark Utils
+
+[[autodoc]] WatermarkDetector
+    - __call__
+