[Cherry-Pick] MTP split draft_tokens into standalone post-processing path(#5205)

[sunlei1024]

#5205

[paddle-bot]

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 97.22222% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release/online/20251131@e0c7ebf). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/output/token_processor.py	96.87%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@                    Coverage Diff                     @@
##             release/online/20251131    #5231   +/-   ##
==========================================================
  Coverage                           ?   59.13%           
==========================================================
  Files                              ?      317           
  Lines                              ?    38711           
  Branches                           ?     5818           
==========================================================
  Hits                               ?    22893           
  Misses                             ?    13992           
  Partials                           ?     1826           

Flag	Coverage Δ
GPU	59.13% <97.22%> (?)

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