[Feature]: Support Eagle Draft Model with different number of KV heads

[MMuzzammil1]

🚀 The feature, motivation and pitch

The current EAGLE implementation raises NotImplementedError (

vllm/vllm/v1/core/kv_cache_utils.py

Line 1098 in 8e8e0b6

raise NotImplementedError

), because of different page_size_bytes calculation (
https://github.com/vllm-project/vllm/blob/main/vllm/v1/kv_cache_interface.py#L68 ) when using a draft model with different num_kv_heads compared to the target model.
However in practice, we can have draft models trained with different num_kv_heads than the target model. Would that be possible to implement this change? Or it would require a lot of architectural changes?

Alternatives

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Additional context

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