Tonepie cat litter box: make dp 128 optional

This is labelled "number" in the QueryThingsDataModel result, with no further
explanation, so not really surprising that it is not always reported.

Issue #1963

custom_components/tuya_local/devices/tonepie_t1pro_catlitterbox.yaml

@@ -18,6 +18,7 @@ primary_entity:
     - id: 128
       type: integer
       name: number
+      optional: true
 secondary_entities:
   - entity: sensor
     name: Times per day