Add DEIMv2 model, image processor, and basic tests

[Vinayaktoor]

What does this PR do?

This PR introduces the DEIMv2 model along with its configuration, image processor, and unit tests. The changes include:

Model Implementation: Added Deimv2ForObjectDetection supporting object detection tasks.

Configuration: Added Deimv2Config for model hyperparameters.

Image Processing: Added Deimv2ImageProcessor to handle preprocessing and postprocessing of images.

Unit Tests: Added tests for configuration, image processing, and model forward pass (tests/models/deimv2/).

This PR builds upon and makes changes to PR by @kekwlboy12469, PR #41291.
Fixes #41211
Fixes missing or incomplete DEIMv2 model integration.

Fixes absence of unit tests for DEIMv2 model and image processor.

Fixes compatibility issues with Transformers pipelines for object detection.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you write any new necessary tests?

Who can review?

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[Rocketknight1]

cc @NielsRogge @yonigozlan

[github-actions]

[For maintainers] Suggested jobs to run (before merge)

run-slow: deimv2

[peacefulotter]

Hi,

Is there still a will to merge this PR at some point ?

I think the implementation is unfinished yet; DEIMV2_PRESETS defines dinov2 as backbone instead of dinov3 and the published model.safetensors doesn't align with the proposed model anyway.

Best

[Rocketknight1]

gentle ping @molbap @NielsRogge @McPatate if anyone wants to take it!