Screen sync light: make switch optional, remove timer

Based on feedback on #264, switch is sometimes not returned, so must be optional to reliably detect the light.  Timer is also often not returned.  Since the entities are not designed to handle all attributes missing, move it to an attribute of the light (where it will be read-only when it is returned).

custom_components/tuya_local/devices/screensync_light.yaml

@@ -5,6 +5,7 @@ primary_entity:
     - id: 20
       type: boolean
       name: switch
+      optional: true
     - id: 21
       type: string
       name: color_mode
@@ -42,7 +43,6 @@ primary_entity:
           range:
             min: 0
             max: 1000
-      optional: true
     - id: 25
       type: hex
       name: effect
@@ -110,19 +110,7 @@ primary_entity:
       type: string
       name: scene
       optional: true
-secondary_entities:
-  - entity: number
-    name: Timer
-    category: config
-    icon: "mdi:timer"
-    dps:
-      - id: 26
-        name: value
-        type: integer
-        range:
-          min: 0
-          max: 86400
-        unit: min
-        mapping:
-          - scale: 60
-            step: 60
+    - id: 26
+      name: timer
+      type: integer
+      optional: true