Lua client: doesn't retain local variables between evaluations and can't use debug module

[russtoku]

@glyh reported in https://github.com/Olical/conjure/pull/495#issuecomment-1586154191:

...further improvement on this maybe try to find if there's a way to implement "real" REPL, because the current implementation is using debug module, that means you either loose local variables across evaluation, or you can't use the debug module when using conjure within neovim.