Add missing @staticmethod decorator to Consts.default()

The method references no instance and takes no self — it was already
being called as Consts.default() throughout the codebase, but without
the decorator Python would pass the first positional argument as self
if it were ever called on an instance.

zz_remux/zz_remux/consts.py

@@ -33,5 +33,6 @@ class Consts:
   lang_codecs  = [ 'subtitle', 'audio' ]
   lang_missing = [ None, lang_undef ]
 
+  @staticmethod
   def default():
     return Consts._default.copy()