fix: access `rope_theta` correctly in `Llama4VisionRotaryEmbedding`
Author: Tcc0403
Pull request: yes

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Fixes #43276

`rope_theta` is no longer accessible via `config.rope_theta` in v5. It has been moved into `config.rope_parameters` dictionary.


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Comments:
run-slow: llama4

This comment contains `run-slow`, running the specified jobs: 

models: ["models/llama4"]
quantizations: []

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_43281). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

## CI Results
[Workflow Run ⚙️](https://github.com/huggingface/transformers/actions/runs/20990425991)

✅ No failing test specific to this PR 🎉 !


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

run-slow: llama4