Expose mlua and other nested dependencies

lib.rs has to do something alon the lines of:
```rust
pub mod mlua {
pub use mlua::*;
}
```

Start in lib.rs and inspect how the mlua dependency is currently made available to users. Add the requested public exposure for mlua and any other nested dependencies identified by the issue, then verify that downstream code can access them through the crate's public API.

Written by the indexing model from the issue text.