Add support for partial rotary embeddings in Phi3 model
Author: garg-amit
Pull request: yes

# What does this PR do?

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This PR adds support for partial rotary embeddings in the Phi3 model. Key changes include:

- Introducing the `partial_rotary_factor` parameter in Phi3Config to control the percentage of queries and keys using rotary embeddings.
- Modifying the `apply_rotary_pos_emb` function to accommodate partial rotary embeddings.
- Updating validation checks in `Phi3Config` to ensure the correct application of the rotary embedding dimensions.


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Comments:
Hi @garg-amit, are there any trained models using this right now?

@Rocketknight1 Not at the moment, but I believe users will have more flexibility when experimenting with different rotary embeddings.
Note: This does not affect the current behavior.

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_35947). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

Thanks! Now, the Phi-4-mini is delivered. :) Justified!