[XPU] Refactor pre process

[cmcamdy]

Motivation

• 前处理优化统一
  【组网】 refactor MTP pre_process ： [MTP] refactor MTP pre_process  #6358
  【算子】speculate_pre_process ： [Speculative Decoding]Reformat input preprocess for spec decode #6501

Modifications

Usage or Command

Accuracy Tests

• benchmark长度没发现明显异常（21B A3B单卡）

• 解码结果发现明显异常

Checklist

• Add at least a tag in the PR title.
  • Tag list: [[FDConfig],[APIServer],[Engine], [Scheduler], [PD Disaggregation], [Executor], [Graph Optimization], [Speculative Decoding], [RL], [Models], [Quantization], [Loader], [OP], [KVCache], [DataProcessor], [BugFix], [Docs], [CI], [Optimization], [Feature], [Benchmark], [Others], [XPU], [HPU], [GCU], [DCU], [Iluvatar], [Metax]]
  • You can add new tags based on the PR content, but the semantics must be clear.
• Format your code, run pre-commit before commit.
• Add unit tests. Please write the reason in this PR if no unit tests.
• Provide accuracy results.
• If the current PR is submitting to the release branch, make sure the PR has been submitted to the develop branch, then cherry-pick it to the release branch with the [Cherry-Pick] PR tag.

[paddle-bot]

Thanks for your contribution!

[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (develop@5780345). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/spec_decode/mtp.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             develop    #6993   +/-   ##
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  Coverage           ?   73.20%           
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  Files              ?      399           
  Lines              ?    56046           
  Branches           ?     8849           
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  Hits               ?    41027           
  Misses             ?    12115           
  Partials           ?     2904           

Flag	Coverage Δ
GPU	73.20% <50.00%> (?)

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