Add model visual debugger (#36798)

* draft of model tracer visualiser

* add context manager in addition to decorator

* add debug utils to init

* move model debugging utils to dedicated file

* add documentation

* protect some imports

* format

* move and protect imports

* format

* doc: improve errors in case of broken dummy imports.

* format

* use automatic torch backend

* update doc

* fix backend

* (TEMP) move to dummies while backend wait

* update documentation

* doc

docs/source/en/internal/model_debugging_utils.md

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+
+# Model debugging toolboxes
+
+This page lists all the debugging and model adding tools used by the library, as well as the utility functions it provides for it.
+
+Most of those are only useful if you are adding new models in the library.
+
+
+## Model addition debuggers
+
+
+### Model addition debugger - context manager for model adders
+
+This context manager is a power user tool intended for model adders. 
+It tracks all forward calls within a model forward and logs a slice of each input and output on a nested Json.
+To note, this context manager enforces `torch.inference_mode()`.
+
+### Rationale
+
+Because when porting models to transformers, even from python to python, model adders often have to do a lot of manual operations, involving saving and loading tensors, comparing dtypes, etc. This small tool can hopefully shave off some time.
+
+### Usage
+
+Add this context manager as follows to debug a model:
+
+```python
+import torch
+from PIL import Image
+import requests
+from transformers import LlavaProcessor, LlavaForConditionalGeneration
+torch.random.manual_seed(673)
+
+# load pretrained model and processor
+model_id = "llava-hf/llava-1.5-7b-hf"
+processor = LlavaProcessor.from_pretrained(model_id)
+model = LlavaForConditionalGeneration.from_pretrained(model_id, low_cpu_mem_usage=True)
+
+# create random image input
+random_image = Image.fromarray(torch.randint(0, 256, (224, 224, 3), dtype=torch.uint8).numpy())
+
+# prompt
+prompt = "<image>Describe this image."
+
+# process inputs
+inputs = processor(text=prompt, images=random_image, return_tensors="pt")
+
+# call forward method (not .generate!)
+with model_addition_debugger_context(model, "optional_path_to_your_output_file.json"):
+    output = model.forward(**inputs)
+
+```
+
+
+[[autodoc]] utils.model_addition_debugger
+
+[[autodoc]] utils.model_addition_debugger_context