Refactor: Use Submodule for efsw Instead of Manual Source Files

[LianYangCn]

The integration of efsw has been updated to use a git submodule rather than directly including individual source files. This makes future updates cleaner and more maintainable.

It’s now linked as a static library via add_subdirectory, and a few minor tweaks were made externally to improve portability without modifying the original source. As a bonus, this also helps to reduce overall build time.

把 efsw 的引用方式改成了 git submodule 的方式，这样以后维护更简单的一些。

efsw 本身支持 cmake, 所以直接在顶层 CMakeLists.cmake 中用 add_subdirectory 来引用更加可维护，只要原作者的代码是可靠的，这里就是可靠的。

另外小改了一下顶层 CMakeLists.cmake 让其更加模块化

[pigpigyyy]

Thank you for your updates and improvements! However, while YueScript's current adoption of the monorepo management approach might introduce some additional complexity for maintainers, it also brings several advantages overall. Firstly, this approach provides us with greater control over third-party dependencies, which is particularly useful when quick adjustments or fixes are needed. Secondly, for users, the monorepo structure makes it more convenient to use the repository and build the code, reducing the management overhead caused by scattered dependencies.

感谢你的更新和改进！不过，YueScript 目前采用 monorepo 的管理方式虽然对维护者来说可能增加了一些复杂性，但从整体上看，它也带来了一些优势。这种方式能够让我们对第三方依赖有更强的掌控能力，尤其是在需要快速调整或修复问题时非常有用。然后对于用户来说，monorepo 的结构让仓库代码的使用和构建变得更加方便，减少了分散依赖带来的源码获取麻烦。