支持用路径列表覆盖 mxsml 动态库搜索路径

[ghangz]

单一路径环境变量在多版本 SDK 共存时不够用。这个改动让 MXSML_LIBRARY_PATH 支持系统路径分隔符列表，可以按优先级提供多个候选目录或文件，适合在 CI、容器和本地开发环境之间复用同一套配置。

这次改动保持默认行为兼容，只在明确需要的场景下引入新的诊断、配置入口或结果输出，避免把沐曦适配相关的问题拖到更晚的运行阶段才暴露出来。

我已经在沐曦 GPU 环境里完成了对应分支验证，并补充或执行了以下相关测试：

• pkg/lib/search_paths_test.go

[gemini-code-assist]

Code Review

This pull request introduces support for configuring multiple SDK search paths via the MXSML_LIBRARY_PATH environment variable. It refactors the library loading logic to dynamically resolve and deduplicate library paths, expanding directory entries to include libmxsml.so while maintaining fallback defaults. Additionally, comprehensive unit tests have been added to verify path list expansion and deduplication. There are no review comments, and I have no feedback to provide.

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