fix: balance Lua module loader stack

[nkbeast]

Summary

• copy the normalized module name out of Lua before constructing lookup paths
• pop the temporary luaL_gsub result from the Lua stack
• use the stable module name for both lookup fallbacks

Validation

• module-loader source assertions passed
• git diff --check — passed

[eduardodoria]

Two commits on main already cover the module loader, both landing after this PR's base: c1594c3 reordered the lookup fallbacks, and fc1815d fixed the std::to_string(char) separator bug.

This PR's diff still carries the old std::to_string form, which is where the conflict comes from.

[nkbeast]

Thanks for the pointers, both commits are in now — kept your separator fix and the lookup order as is.

What's left in this PR is just the stack balance: luaL_gsub pushes the substituted name onto the Lua stack and nothing popped it, so every require() left one slot behind. The name is copied into a std::string before the pop so the pointer stays valid afterwards.

[nkbeast]

Closing this — your two commits covered the real problems here, and looking at the rebased diff the only thing left was the luaL_gsub pop, which the normal require cleanup already handles anyway. Thanks for the quick pointers on which commits landed.