Cohere: update RoPE structure

[gante]

What does this PR do?

This PR propagates the updates to the RoPE structure to cohere -- the logic for RoPE was abstracted into a separate module for llama3.1 (#32135). Using the new structure, a model has access to all RoPE scaling strategies.

While touching the modeling code, I've taken the liberty to:

1. update copied from statements, which were disabled in previous PRs;
2. update (postpone) deprecation messages to ensure deprecated features are removed from all models in the same version.

✅ all slow tests passing

---

Note: #31999 was originally open to migrate all modern RoPE models into the upgraded structure. However, working on cohere, I noticed that there may be important implementation differences in RoPE. As such, I'll be opening multiple PRs, batching similar RoPE implementations together.

[gante]

This is copy/paste from llama

[gante]

Aside from the line highlighted with a comment, this is copy/paste from llama

[gante]

@LysandreJik a PR like this one will be open for a few more modern models. Since part of the changes consists of having a global view of the model to update the copied from statements, would you like me to update the import structures as well? 🤗

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[LysandreJik]

This looks clean, nice to reuse the llama code

[LysandreJik]

@LysandreJik a PR like this one will be open for a few more modern models. Since part of the changes consists of having a global view of the model to update the copied from statements, would you like me to update the import structures as well? 🤗

No need to updat the import structure for now!