docs: def keys(self, prefix=None):
          """List all keys, with optional prefix filtering."""
          query = Setting.query
          if prefix:
              query = query.filter(Setting.key.startswith(prefix))
  
          # don't use iteritems: 'value' require little processing whereas we only
          # want 'key'
          return [i[0] for i in query.yield_per(1000).values(Setting.key)]