feat(number): allow max and min dps to be optional

Fall back on using the range of the value dp when maximum and minimum
are configured, but not reported by the device.

For implementation of idea in discussion #3373

custom_components/tuya_local/number.py

@@ -70,14 +70,18 @@ class TuyaLocalNumber(TuyaLocalEntity, NumberEntity):
     @property
     def native_min_value(self):
         if self._min_dps is not None:
-            return self._min_dps.get_value(self._device)
+            minimum = self._min_dps.get_value(self._device)
+            if minimum is not None:
+                return minimum
         r = self._value_dps.range(self._device)
         return DEFAULT_MIN_VALUE if r is None else r[0]
 
     @property
     def native_max_value(self):
         if self._max_dps is not None:
-            return self._max_dps.get_value(self._device)
+            maximum = self._max_dps.get_value(self._device)
+            if maximum is not None:
+                return maximum
         r = self._value_dps.range(self._device)
         return DEFAULT_MAX_VALUE if r is None else r[1]