[Refactor][EAGLE] 2/N: load model and generate token (#5437)

### What this PR does / why we need it?
1. Refactor eagle and mtp function: load_model and generate_token_ids
2. Remove redundant code in mtp and eagle file
3. Refactor the UT of file

2/N of Refactor and merge mtp and eagle
Relational RFC: https://github.com/vllm-project/vllm-ascend/issues/5467

### Does this PR introduce _any_ user-facing change?
no

### How was this patch tested?
ut and tests

- vLLM version: release/v0.13.0
- vLLM main:
81786c8774

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Signed-off-by: lilinsiman <lilinsiman@gmail.com>

docs/source/user_guide/feature_guide/index.md

@@ -12,6 +12,7 @@ structured_output
 lora
 eplb_swift_balancer
 netloader
+Multi_Token_Prediction
 dynamic_batch
 kv_pool
 external_dp