[WIP][Model Runner V2] Enable mamba align for spec decode

[TheEpicDolphin]

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[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @TheEpicDolphin.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[gemini-code-assist]

Code Review

This pull request introduces support for hybrid Mamba-Attention models in the V1 engine, specifically enabling speculative decoding in 'align' mode through a new MambaHybridModelState and dual-indexing logic in Mamba kernels. It also updates KV cache management and refactors multimodal registry error handling to be more robust. Review feedback suggests replacing redundant assertions in the new model state implementation with explicit error handling or type guards.

[gemini-code-assist]

The assertions assert req_states is not None and assert scheduled_spec_decode_tokens is not None are redundant because these arguments are already typed as RequestState | None and dict[str, list[int]] | None respectively, and the logic below relies on them being present. If they are None, the code will fail with an AttributeError anyway. It is better to handle the None case explicitly or use a type guard.

[gemini-code-assist]

The assertions assert self.last_kv_cache_config is not None and assert self.last_block_tables is not None are redundant. If these are None, the code will fail with an AttributeError. It is better to handle the None case explicitly or ensure the state is initialized correctly.