Support requiring native modules

[jkelaty-rbx]

Note: I'm mostly leaving this open for historical context, though I am also happy to revive this PR if there's interest in moving forward with it.

Motivation

Enables users to write C/C++ libraries that extend Lute with native functionality (e.g., bindings to libgit2, SQLite, image processing) without forking Lute. Native modules follow the same luteopen_* convention as built-in @lute/ modules and are loaded through the standard require() path.

Summary

• Extends require() to load native shared libraries (.dylib, .so, .dll) from disk via uv_dlopen/uv_dlsym
• Entry point convention: libfoo.dylib → extern "C" int luteopen_foo(lua_State* L)
• Library handles are anchored in a _NATIVELIBS registry table and closed when the lua_State is torn down
• Includes a working example at examples/native-extension/
• Type checking is supported via a types file embedded in the shared object