Fix Prometheus casting issues (#22282)

## Description:

Fix Prometheus casting issues

**Related issue (if applicable):** fixes #8659.
## Checklist:
  - [x] The code change is tested and works locally.
  - [x] Local tests pass with `tox`. **Your PR cannot be merged unless tests pass**
  - [x] There is no commented out code in this PR.

homeassistant/components/prometheus/__init__.py

@@ -103,6 +103,16 @@ class PrometheusMetrics:
                 full_metric_name, documentation, labels)
             return self._metrics[metric]
 
+    @staticmethod
+    def state_as_number(state):
+        """Return a state casted to a float."""
+        try:
+            value = state_helper.state_as_number(state)
+        except ValueError:
+            _LOGGER.warning("Could not convert %s to float", state)
+            value = 0
+        return value
+
     @staticmethod
     def _labels(state):
         return {
@@ -130,7 +140,7 @@ class PrometheusMetrics:
             self.prometheus_client.Gauge,
             'State of the binary sensor (0/1)',
         )
-        value = state_helper.state_as_number(state)
+        value = self.state_as_number(state)
         metric.labels(**self._labels(state)).set(value)
 
     def _handle_input_boolean(self, state):
@@ -139,7 +149,7 @@ class PrometheusMetrics:
             self.prometheus_client.Gauge,
             'State of the input boolean (0/1)',
         )
-        value = state_helper.state_as_number(state)
+        value = self.state_as_number(state)
         metric.labels(**self._labels(state)).set(value)
 
     def _handle_device_tracker(self, state):
@@ -148,7 +158,7 @@ class PrometheusMetrics:
             self.prometheus_client.Gauge,
             'State of the device tracker (0/1)',
         )
-        value = state_helper.state_as_number(state)
+        value = self.state_as_number(state)
         metric.labels(**self._labels(state)).set(value)
 
     def _handle_person(self, state):
@@ -157,7 +167,7 @@ class PrometheusMetrics:
             self.prometheus_client.Gauge,
             'State of the person (0/1)',
         )
-        value = state_helper.state_as_number(state)
+        value = self.state_as_number(state)
         metric.labels(**self._labels(state)).set(value)
 
     def _handle_light(self, state):
@@ -171,7 +181,7 @@ class PrometheusMetrics:
             if 'brightness' in state.attributes:
                 value = state.attributes['brightness'] / 255.0
             else:
-                value = state_helper.state_as_number(state)
+                value = self.state_as_number(state)
             value = value * 100
             metric.labels(**self._labels(state)).set(value)
         except ValueError:
@@ -183,7 +193,7 @@ class PrometheusMetrics:
             self.prometheus_client.Gauge,
             'State of the lock (0/1)',
         )
-        value = state_helper.state_as_number(state)
+        value = self.state_as_number(state)
         metric.labels(**self._labels(state)).set(value)
 
     def _handle_climate(self, state):
@@ -209,7 +219,7 @@ class PrometheusMetrics:
             'climate_state', self.prometheus_client.Gauge,
             'State of the thermostat (0/1)')
         try:
-            value = state_helper.state_as_number(state)
+            value = self.state_as_number(state)
             metric.labels(**self._labels(state)).set(value)
         except ValueError:
             pass
@@ -232,7 +242,7 @@ class PrometheusMetrics:
                                state.entity_id)
 
         try:
-            value = state_helper.state_as_number(state)
+            value = self.state_as_number(state)
             if unit == TEMP_FAHRENHEIT:
                 value = fahrenheit_to_celsius(value)
             _metric.labels(**self._labels(state)).set(value)
@@ -249,7 +259,7 @@ class PrometheusMetrics:
         )
 
         try:
-            value = state_helper.state_as_number(state)
+            value = self.state_as_number(state)
             metric.labels(**self._labels(state)).set(value)
         except ValueError:
             pass