Add a DISABLE_DREAMLUAU define, for disabling dreamluau at compile-time (#89359)

## About The Pull Request

this adds a new define, `DISABLE_DREAMLUAU` (commented out by default),
which does... exactly what it says on the tin. it fully disables any
dreamluau-related code (the "Open Lua Editor" admin verb is left in,
albeit just giving the user a warning saying Lua is disabled, just so
there's no confusion about the verb itself being missing)

when compiling with OpenDream outside of CI (so dreamluau code will
still be linted), `DISABLE_DREAMLUAU` will be defined by default, tho.

## Why It's Good For The Game

makes OpenDream testing easier

## Changelog

no user-facing changes. or even code changes for most cases.

code/modules/admin/topic.dm

@@ -1699,6 +1699,7 @@
 			return
 		return usr.client?.mark_datum(datum_to_mark)
 
+#ifndef DISABLE_DREAMLUAU
 	else if(href_list["lua_state"])
 		if(!check_rights(R_DEBUG))
 			return
@@ -1715,6 +1716,7 @@
 				editor.force_view_chunk = log_entry["chunk"]
 				editor.force_modal = "viewChunk"
 		editor.ui_interact(usr)
+#endif
 
 	else if(href_list["show_paper"])
 		if(!check_rights(R_ADMIN))