There may not be lua-specific code-tags, but is there any reason why you couldn't simply use the generic "[ code ] ... [ /code ]" tags (without the spaces, obviously)?
Only a limited set of file-extensions are permitted as post-attachments (for security, I believe?), but these do include standard archive-formats such as .rar, .zip, etc.
You can also change a file's extension manually to a permitted format, e.g. ".txt" (I think that one's permitted, but I can't find a list right now), allowing it to be uploaded to CFC — with the understanding that anyone who then downloads that file would need to change the extension back to the original.