Add Image Processor Fast RT-DETR (#34354)

* add fast image processor rtdetr

* add gpu/cpu test and fix docstring

* remove prints

* add to doc

* nit docstring

* avoid iterating over images/annotations several times

* change torch typing

* Add image processor fast documentation

docs/source/en/model_doc/rt_detr.md

@@ -46,7 +46,7 @@ Initially, an image is processed using a pre-trained convolutional neural networ
 >>> from PIL import Image
 >>> from transformers import RTDetrForObjectDetection, RTDetrImageProcessor
 
->>> url = 'http://images.cocodataset.org/val2017/000000039769.jpg' 
+>>> url = 'http://images.cocodataset.org/val2017/000000039769.jpg'
 >>> image = Image.open(requests.get(url, stream=True).raw)
 
 >>> image_processor = RTDetrImageProcessor.from_pretrained("PekingU/rtdetr_r50vd")
@@ -95,6 +95,12 @@ A list of official Hugging Face and community (indicated by 🌎) resources to h
     - preprocess
     - post_process_object_detection
 
+## RTDetrImageProcessorFast
+
+[[autodoc]] RTDetrImageProcessorFast
+    - preprocess
+    - post_process_object_detection
+
 ## RTDetrModel
 
 [[autodoc]] RTDetrModel