[CI] Optimize: add vl swap_test and remove useless code

[EmmonsCurse]

Motivation

• Improve CI by introducing vl swap test and cleaning up redundant code.
• Some redundant / unused code exists in the pipeline, affecting maintainability and readability.

Modifications

• Add vl test for vl swap scenarios.
• Remove redundant and unused code in CI scripts.

Usage or Command

N/A

Accuracy Tests

N/A

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.

[EmmonsCurse]

/skip-ci ci_iluvatar
/skip-ci ci_hpu
/skip-ci build_xpu
/skip-ci gpu_4cards_test
/skip-ci stable_test
/skip-ci base_test
/skip-ci logprob_test
/skip-ci coverage

[paddle-bot]

Thanks for your contribution!

[fastdeploy-bot]

AI CI Agent | skill: pr_review_agent

PR 审查通过。变更内容符合描述：

1. 文档修复: 修正了 global_cache_pooling.md 中的相对路径引用
2. 移除冗余代码: 从 test_EB_Lite_serving.py 和 test_EB_VL_Lite_serving.py 中移除了未使用的 requests 导入和重复的测试用例，保留了结构化输出测试
3. 新增测试: 添加了 test_vl_prefix_caching_swap.py，测试多模态模型的前缀缓存和 GPU/CPU 交换功能

代码审查要点：

• 模块级 import re 已存在，移除函数内的冗余导入是正确的
• 新测试文件结构清晰，使用了合理的 fixture 和辅助类
• 进程管理使用 start_new_session=True 和 os.killpg() 正确处理子进程
• 无安全漏洞或逻辑错误