[FIX] fix wrong indexing for hidden states when prefix-cache take effect

[Dutch-voyage]

Motivation

return_hidden_states=True does not return prefilled hidden_states as expected.
see relevant issue #4997

Modifications

In scheduler_output_processor_mixin.py:116
change

req.hidden_states.append(
    logits_output.hidden_states[
        hidden_state_offset : (
            hidden_state_offset := hidden_state_offset
            + len(req.origin_input_ids)
        )
    ]
    .cpu()
    .clone()
    .tolist()
)

to

req.hidden_states.append(
    logits_output.hidden_states[
        hidden_state_offset : (
            hidden_state_offset := hidden_state_offset
            + req.extend_input_len
        )
    ]
    .cpu()
    .clone()
    .tolist()
)

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