Revert to using standard Lua instead of Luau headers

[stayaway245]

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[mentatbot]

I've reviewed the changes in this PR which reverts from using internal Luau headers to standard Lua headers. Here's my assessment:

Changes Overview

• Modified the GitHub workflow to install and use standard Lua instead of relying on bundled Luau headers
• Updated the CMake configuration to find and use external Lua headers in standard system paths
• Corrected include statements in source/lfs.c to use standard Lua headers

Technical Comments

This change appears to be a correct and well-implemented approach for several reasons:

1. Improved Standardization: Using standard Lua headers rather than Luau-specific ones makes the project more compatible with standard Lua installations and ecosystems.

2. Better Build Reproducibility: By using system-provided Lua libraries through standard package management (Homebrew), the build becomes more reproducible across different environments.

3. Clearer Dependency Management: The approach of explicitly finding and setting up Lua dependencies is more transparent than relying on bundled headers.

4. Compatibility: The changes include fallback mechanisms and proper conditional includes to support various system configurations.

Since this PR has already been merged and is relatively straightforward, there's no additional action needed. The code should now build correctly with standard Lua instead of requiring Luau-specific headers.