### What this PR does / why we need it?
We optimized the _prepare_input method in eagle_proposer and no longer
use the _prepare_eagle_input_sequential method, improving the
performance of eagle-3.
### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
```
python3 -m vllm.entrypoints.openai.api_server
--host 0.0.0.0
--port 13963
--dtype bfloat16
--model meta-llama/Llama-3.1-8B-Instruct
--served-model-name Llama-3.1-8B-Instruct
--tensor-parallel-size 1
--gpu-memory-utilization 0.85
--max-model-len 32768
--trust-remote-code
--seed 42
--no-enable-prefix-caching
--speculative_config '{"method":"eagle3","model":"yuhuili/EAGLE3-LLaMA3.1-Instruct-8B","num_speculative_tokens":2,"draft_tensor_parallel_size":1}'
```
Co-authored-by: QilaiZhang (245706640@qq.com )
- vLLM version: v0.11.0rc3
- vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.0
Signed-off-by: lio <1983142975@qq.com>
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