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/verbs/lua/_wrappers.dm

@@ -1,3 +1,4 @@
+#ifndef DISABLE_DREAMLUAU
 /proc/wrap_lua_get_var(datum/thing, var_name)
 	SHOULD_NOT_SLEEP(TRUE)
 	if(thing == world)
@@ -46,3 +47,4 @@
 	var/result = list("status" = "print", "message" = print_message)
 	INVOKE_ASYNC(target_state, TYPE_PROC_REF(/datum/lua_state, log_result), result, TRUE)
 	log_lua("[target_state]: [print_message]")
+#endif