Add benchmark support using -b

Program.cs

@@ -1,9 +1,18 @@
-
-using System.Diagnostics;
+using System.Diagnostics;
 using System.Reflection;
+using AdventOfCode;
 using AdventOfCode.Days;
+using BenchmarkDotNet.Running;
 using Spectre.Console;
 
+// Benchmark
+if (args is ["--bench" or "-b"])
+{
+    BenchmarkRunner.Run<DayBenchmark>();
+    Environment.Exit(0);
+}
+
+// Normal run
 var days = Assembly.GetAssembly(typeof(Day))!.GetTypes()
     .Where(t => t.IsAssignableTo(typeof(Day)) && t.GetConstructor(Type.EmptyTypes) != null && !t.IsAbstract)
     .Select(t => (Day)Activator.CreateInstance(t)!);