Change to MetricsProviders.

 * Instead of throw InvalidOperationException, convert to return null so they can be used inside Workflows.

src/HouseofCat.Metrics/OpenTelemetry/OpenTelemetryMetricsProvider.cs

@@ -126,25 +126,25 @@ public void DecrementCounter(string name, string unit = null, string description
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public IDisposable Duration(string name, bool microScale = false, string unit = null, string description = null)
     {
-        throw new NotImplementedException();
+        return null;
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public IDisposable Track(string name, string unit = null, string description = null)
     {
-        throw new NotImplementedException();
+        return null;
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public MultiDispose TrackAndDuration(string name, bool microScale = false, string unit = null, string description = null)
     {
-        throw new NotImplementedException();
+        return null;
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public MultiDispose Trace(string name, string unit = null, string description = null)
     {
-        throw new NotImplementedException();
+        return null;
     }
 
     #endregion

src/HouseofCat.Metrics/Prometheus/PrometheusMetricsProvider.cs

@@ -194,7 +194,7 @@ public MultiDispose TrackAndDuration(string name, bool microScale = false, strin
 
     public MultiDispose Trace(string name, string unit = null, string description = null)
     {
-        throw new NotImplementedException();
+        return null;
     }
 
     #endregion

version.props

@@ -1,7 +1,7 @@
 <Project>
   <PropertyGroup>
-    <Version>3.1.2</Version>
-    <AssemblyVersion>3.1.2</AssemblyVersion>
-    <FileVersion>3.1.2</FileVersion>
+    <Version>3.1.3</Version>
+    <AssemblyVersion>3.1.3</AssemblyVersion>
+    <FileVersion>3.1.3</FileVersion>
   </PropertyGroup>
 </Project>