fix(examples): add backwards-compatible fallback for transformers>=5.0 in ViT/DeiT models

[Aamod007]

What type of PR is this?
/kind bug

What this PR does / why we need it:
This PR fixes compatibility with transformers >= 5.0 in the vit.py and deit.py examples.

In transformers 5.x, several ViT classes were removed or refactored (e.g. ViTSelfAttention, ViTSelfOutput, ViTIntermediate, ViTOutput). This previously caused an ImportError preventing the models from running.

This PR implements a robust, backwards-compatible fallback mechanism: it attempts to import the original components, and upon encountering an ImportError, it defines the necessary internal ViT block classes directly using standard nn.Module. This ensures that Ianvs runs flawlessly on both legacy and modern transformers environments without breaking changes.

Which issue(s) this PR fixes:
Fixes #509

Special notes for your reviewer:
N/A

[kubeedge-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Aamod007
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[gemini-code-assist]

Code Review

This pull request introduces a fallback mechanism in vit.py to define local implementations of ViT components (ViTSelfAttention, ViTSelfOutput, ViTIntermediate, and ViTOutput) in case they cannot be imported from the transformers library, and updates deit.py to use these local imports. Feedback was provided pointing out a critical bug in the fallback ViTOutput implementation, which is missing the residual connection addition (hidden_states + input_tensor) and would lead to incorrect model outputs.

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[Aamod007]

/assign @jaypume

[Aamod007]

/assign @jaypume