feat: metrics test.

Game/Metrics/MetricsHandler.cs

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+using System;
+using System.Diagnostics.Metrics;
+using System.Reflection;
+using GodotHostTest.Interfaces;
+using OwofGames.GodotHost;
+using R3;
+
+namespace GodotHostTest.Game.Metrics;
+
+public class MetricsHandler(IMeterFactory meterFactory, ITargetEventBus targetEventBus) : IHostLifetime
+{
+    public static readonly string MeterName;
+    private static readonly string? MeterVersion;
+    private IDisposable? _disposables;
+
+    static MetricsHandler()
+    {
+        var assemblyName = Assembly.GetExecutingAssembly().GetName();
+        MeterName = assemblyName.Name!;
+        MeterVersion = assemblyName.Version?.ToString();
+    }
+
+    public void Startup()
+    {
+        // create meter
+        var assemblyName = Assembly.GetExecutingAssembly().GetName();
+        var meterName = assemblyName.Name!;
+        var meterVersion = assemblyName.Version?.ToString();
+        var meter = meterFactory.Create(meterName, meterVersion);
+
+        // create instruments
+        var hitTargetsCounter =
+            meter.CreateCounter<int>("targets.hit", description: "number of targets hit");
+        var missedTargetsCounter =
+            meter.CreateCounter<int>("targets.missed", description: "number of targets missed");
+
+        // feed instruments data, and contextually create the disposable to clean up at shutdown time
+        _disposables = Disposable.Combine(
+            targetEventBus.Hit.Subscribe(_ => hitTargetsCounter.Add(1)),
+            targetEventBus.TimedOut.Subscribe(_ => missedTargetsCounter.Add(1)),
+            meter
+        );
+    }
+
+    public void Shutdown()
+    {
+        _disposables?.Dispose();
+        meterFactory.Create("godot-host-test")?.Dispose();
+    }
+}

Game/Metrics/MetricsHandler.cs.uid

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+uid://5ramu7es1104