[Quantization] Support w4afp8 DeepEP low latency two stage

[Sunny-bot1]

Motivation

为w4afp8量化推理支持DeepEP两阶段通信优化

Modifications

与low_latency_dispatch保持一致，在low_latency_dispatch_two_stage和low_latency_combine_two_stage增加quant_group_size参数区分激活的量化粒度：

• w4afp8：激活per-token量化，quant_group_size=-1
• fp8：激活per-token-group量化：quant_group_size=128（default）

依赖最新Paddle（12.17之后的包含commit 5e27f876c1945ed23cb3f1b59ec22f9de96ee056），相关PR：PaddlePaddle/Paddle#76863

Usage or Command

export FD_ENABLE_MULTI_API_SERVER=1
python -m fastdeploy.entrypoints.openai.multi_api_server \
       --args --tensor-parallel-size 1 \
       --data-parallel-size 8 \
       --enable-expert-parallel \
       --use-internode-ll-two-stage \
       --quantization w4afp8 \
       --load-choices default 
       ...

Accuracy Tests

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 0% with 3 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (develop@21fa2ba). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/model_executor/layers/moe/ep.py	0.00%	2 Missing ⚠️
...l_executor/layers/moe/fused_moe_cutlass_backend.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             develop    #5608   +/-   ##
==========================================
  Coverage           ?   62.14%           
==========================================
  Files              ?      329           
  Lines              ?    41553           
  Branches           ?     6345           
==========================================
  Hits               ?    25822           
  Misses             ?    13793           
  Partials           ?     1938           

Flag	Coverage Δ
GPU	62.14% <0.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.