Commit benchmark to source

Co-authored-by: Andrei Zavatski <megaman9919@gmail.com>

osu.Game.Benchmarks/BenchmarkUnstableRate.cs

@@ -0,0 +1,31 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Collections.Generic;
+using BenchmarkDotNet.Attributes;
+using osu.Framework.Utils;
+using osu.Game.Rulesets.Objects;
+using osu.Game.Rulesets.Scoring;
+
+namespace osu.Game.Benchmarks
+{
+    public class BenchmarkUnstableRate : BenchmarkTest
+    {
+        private List<HitEvent> events = null!;
+
+        public override void SetUp()
+        {
+            base.SetUp();
+            events = new List<HitEvent>();
+
+            for (int i = 0; i < 1000; i++)
+                events.Add(new HitEvent(RNG.NextDouble(-200.0, 200.0), RNG.NextDouble(1.0, 2.0), HitResult.Great, new HitObject(), null, null));
+        }
+
+        [Benchmark]
+        public void CalculateUnstableRate()
+        {
+            _ = events.CalculateUnstableRate();
+        }
+    }
+}