[Feature] get_output_kv_signal blocking read mode & send_first_token

[ST-XX]

Motivation

layer_wise 传输实现以前是循环查询，忙等待逻辑，可能会触发10ms 的等待时间。对于 GPU-RDMA-Direct 传输的 us延迟是数量级的差别。修改为阻塞式读取
调整 首 token发送与资源回收的先后顺序。这里还有 ms级别的优化空间，
走 GPU-RDMA ，数据量较小的话，基本是算完就传输完成了。tokenizer_processor 的流程目前是拖慢了整体流水线。

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Modifications

blocking

Usage or Command

• ENABLE_V1_KVCACHE_SCHEDULER=0 bash start_v1_tp1.sh

Accuracy Tests

test case:

• ENABLE_V1_KVCACHE_SCHEDULER=0 bash start_v1_tp1.sh
• ENABLE_V1_KVCACHE_SCHEDULER=1 bash start_v1_tp1.sh
• --cache-transfer-protocol "rdma"

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.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 69.23077% with 4 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (develop@24ffa7c). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
fastdeploy/output/token_processor.py	57.14%	1 Missing and 2 partials ⚠️
fastdeploy/cache_manager/cache_messager.py	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             develop    #5836   +/-   ##
==========================================
  Coverage           ?   67.33%           
==========================================
  Files              ?      349           
  Lines              ?    45050           
  Branches           ?     6938           
==========================================
  Hits               ?    30335           
  Misses             ?    12477           
  Partials           ?     2238           

Flag	Coverage Δ
GPU	67.33% <69.23%> (?)

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[paddle-bot]

Thanks for your contribution!