Experimental Kernel Switching Support / 实验性内核切换支持

This fork introduces experimental kernel switching, enabling use of pdf2zh_next—a significantly enhanced kernel for pdf2zh.
这个分叉引入了实验性内核切换, 使得 pdf2zh_next 能够显著增强内核的使用，用于 pdf2zh。

This pull request is proposed for this breaking change in the structure and is not intentionally made to be merged at this stage.
这个拉取请求是针对结构中的这种突破性变化提出的，并非有意在此阶段进行合并。

The refreshed GUI requires this function of switching between kernels.
更新后的 GUI 需要这种内核间切换功能。

✨ Feature / 特性

• Users can now specify the pdf2zh_next kernel by the genius engineer awwaawwa through a simple CLI argument: --kernel experimental
  现在，用户可以通过一个简单的 CLI 参数，指定天才工程师 awwaawwa 的 pdf2zh_next 内核：--kernel experimental（实验性内核

🔧 Changes / 变更

• A dedicated folder containing the functions provided by pdf2zh_next is added under: ./kernel/experimental
  在./kernel/experimental下添加了一个包含pdf2zh_next提供的功能的专用文件夹。

• An executable shortcut for pdf2zh_next has been added to the main installation configuration, simplifying integration.
  在主安装配置中添加了 pdf2zh_next 的快捷可执行文件，简化了集成过程。

⚠️ Breaking Changes / 突破性变革

• The babeldoc library has been upgraded to match the refreshed upstream version.
  Babeldoc 库已经升级，以匹配上游。

Tests passed / 通过测试

• Although this update could introduce new bugs, the main functionality has been tested against the provided test files.
  尽管这个更新可能会引入新的 bug, 但主要功能已经根据提供的测试文件进行了测试。
• The original use case of the pdf2zh program is not affected.
  pdf2zh "程序的原始使用不受影响。