[V1] Do not allocate beyond the max_model_len

[WoosukKwon]

This PR fixes a bug in V1 KV cache manager that allocates more than max_model_len // block_size blocks for a request. This is not only inefficient but also illegal because the block table has a fixed shape of [max_num_reqs, max_model_len // block_size].

[github-actions]

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[comaniac]

Otherwise LGTM. Also where do we reject too long requests? Seems like the scheduler doesn't do that?

[WoosukKwon]

where do we reject too long requests? Seems like the scheduler doesn't do that?

@comaniac You're right. V1 doesn't have it now.

[comaniac]

where do we reject too long requests? Seems like the scheduler doesn't do that?

@comaniac You're right. V1 doesn't have it now.

I see. We could add that later. Meanwhile could you add a TODO in this PR as a reminder?

[WoosukKwon]

I see. We could add that later. Meanwhile could you add a TODO in this PR as a reminder?

@comaniac Good point. Added. PTAL.